Burma, struggling with a rapidly deteriorating economy and the imminent danger of food shortages, has embarked on the most radical trade and monetary changes in a quarter of a century.

The steps have provoked student protests and led to confusion in the marketplace. All educational institutions have been closed indefinitely, according to Government radio broadcasts.

Over the last two weeks, the Government of Ne Win, who seized power in 1962, announced without warning that all restrictions on trade in staple foods were being lifted to get needed supplies into circulation.

Burmese were told on Sept. 1 that they are now allowed to buy, sell, store and transport rice, corn and bean crops free of Government control. Since 1966, most commodity prices and distribution systems have been set by the Ne Win administration. Some Currency Withdrawn

In addition, farmers will be required to pay taxes in foodstuffs, not cash, the Government said.

On Sept. 5, all currency notes except small denominations were withdrawn from circulation.

Reports reaching here from Rangoon, the Burmese capital, say that the cumulative effect of these decrees has thrown trade into confusion, with many shops closed. Students Voice Frustration

For the first time since 1974, there have been student disturbances in Rangoon, apparently prompted by the withdrawal of 25, 35 and 75 kyat notes, leaving only small bills in circulation. An American dollar is worth about 6.6 kyat at official rates, and six or seven times that amount on the black market.

On Sept. 6, a sweeping Government ordinance closed all universities, colleges, technical institutes, medical and dental schools, high schools, primary schools and part-time educational institutions, such as night schools and vocational schools, until further notice.

Students were reported to be voicing the frustrations of a wider public. Burmese interviewed earlier this year say many people have still not received new notes for bills turned in in 1985, when the Government changed the currency to cut down on black market trade. Students Join the Unemployed

Students, who say there are fewer and fewer jobs being created to meet their qualifications as the economy stumbles, are joining the unemployed or underemployed in large numbers.

Many are the children of parents who were formerly middle class, but who have seen their professions shrink under a military-dominated ''Burmese Way to Socialism,'' the official credo of the ruling Burmese Socialist Program Party. Most Burmese have been forced into some black market buying or selling to survive. High Literacy Level

Before the 25th anniversary, in March, of General Ne Win's seizure of power from a democratically elected government, Burma had asked the United Nations to classify the country as being among the ''least developed.''

Burma, with a high literacy level, is thought to have a per capita gross national product of about $180 a year -more than Vietnam's estimated $160 but far less than neighboring Thailand's $600. In recent months, the drought that is affecting much of Asia has added to food-production problems caused by what development specialists call a badly conceived Government rice-distribution system.

Signs that Burma's economy may be reaching a crisis came first in mid-August, when General Ne Win, as chairman of the Socialist Program Party, suddenly convened Government officials and announced that they must ''stop hiding the facts'' about the nation's economic failures.

International aid experts fear that if a significant part of this year's rice crop is lost, Burma - once one of the world's leading rice producers - could face famine for the first time. With few roads and minimal rail and air links, emergency relief could prove difficult.

Western diplomats said today that an outward calm had returned to Burma after clashes between demonstrators and the police and military 10 days ago, but that tension remained unusally high.

''There's a feeling of more to come,'' said a diplomat who returned recently from Rangoon, the Burmese capital.

Rangoon, Pegu, Moulmein, Prome and perhaps other cities are reported to remain under a 60-day, 6 P.M.-to-6 A.M. curfew imposed after the severe clashes on June 21.

All universities, colleges and high schools are said to be closed, and out-of-town students have been ordered to return to their villages. The military is out in force in the capital, a diplomat said. Toll Called Unreported

The clashes last month were set off by student demonstrations in the capital and other cities. The Government said nine people, including six policemen, were killed in the rioting in Rangoon, Mandalay and Pegu. Seventy-seven people, including 10 students, were reported arrested.

The diplomats and other experts on Burmese affairs say they believe both totals to be well short of the truth. But with a cowed population and the press wholly under Government control, reliable information is unavailable.

Some reports reaching here said unease was apparent not only among opponents of Gen. Ne Win's 26 years of draconian rule, but for the first time also in the military, which is the pillar of the Government.

The retired general, who seized power in a coup in 1962 and whose policy is called the Burmese Way to Socialism, dominates the country of 38 million through his position as chairman of the sole legal mass organization, the Burmese People's Program Party, and his unchallenged control over the military.

Diplomats and others interviewed, who are privy to the reporting of embassies in Rangoon or to word reaching Burmese here from relatives and friends inside their largely isolated country, said the military was reacting nervously to the widening and increasingly open popular resentment against the army that was evident in the clashes that took place last week. Further Trouble Expected

Evidence of more widespread support for student demonstrators than in the past is another element leading to an expectation of further troubles ahead for the Government.

A senior diplomat said officers feared that the military's deepening alienation from the people jeopardizes its expectation of continued military rule after General Ne Win leaves the scene. The general is at least 76 years old and is believed to have had two heart attacks or strokes.

At the same time, however, an embassy in Rangoon said there were no signs of splits within the army. ''The monolith appears intact,'' the embassy said.

Reporting about Burma is limited to secondary sources. This correspondent, like others known to be journalists, was refused a visa, as the Government has clearly increased its measures to guard against reporters even beyond its usual vigilance.

Visitors, resident diplomats and international officials say that since last year Burma's economic plight has severely worsened. As a result, opposition to General Ne Win's rule is reported to have spread from students and the deprived professional classes to the population at large. A 'Least-Developed Nation'

After a quarter century of the general's rule, the United Nations last year assigned Burma, a country rich in natural resources and talent, to its category of ''least-developed nations.'' Once the world's leading rice exporter, shipments abroad shrank last year to 150,000 tons, the lowest since independence from British rule in 1948. Distribution difficulties have led for the first time to reports of local food shortages.

Much of Burma's wealth in gemstones and precious woods leaves the countryside through border areas controlled by insurgents, without benefit to the national treasury. Much of what remains is said to be lost to the nation through widespread corruption from top to bottom of the military-dominated administrative structure.

The foreign debt stands near $4 billion; foreign-exchange reserves cover less than one month of imports.

Diplomats reported that this year, for the first time, ordinary citizens have demonstrated support for student protests.

Even Government announcements stressed that students, traditionally the vanguard of opposition, were ''a small group'' among ''a majority of civilians.'' Official reports said protesters wielding swords, sticks and slingshots had burned a police station, destroyed Government offices, factories, textile mills, stores and movie theaters and set fire to police family quarters. Police Brutality Reported

Diplomats reported considerable police brutality against the demonstrators. One unconfirmed report to an embassy asserted that 70 people, including 26 policemen, had been killed in Pegu alone.

The first incidents of open protest that rose to Burma's impoverished surface, largely placid since the last wave of serious student unrest in 1974, occurred last September. The Government, without warning, reduced to the value of scrap paper the highest denominations of banknotes. Bills that were worth $11.25, $5.25 and $3.75 were declared invalid and not exchangeable for new currency.

No explanation was given, but the action, which invalidated 60 to 80 percent of the money in circulation, was thought to have been directed partly against the extensive black market, which is at least as large as the official economy. Other targets of the action were believed to be inflation, which is very high but hard to calculate because of the extent of the unrecorded economy, and the cash holdings of the political and ethnic insurgents.

Whatever its main goal, the invalidation of the money also destroyed much of the nest eggs of the majority in a poor nation, whose people have no faith in the Government-owned savings institutions and keep their reserves in cash or gold.

Still, said a writer who specializes in Burma and has good contacts in the country, when students demonstrated in Rangoon and Mandalay and urged other Burmese to join, the response was feeble and the protests waned quickly. Started in Teahouse Brawl

But ill feelings persisted among students and spilled over into mass demonstrations on March 12. They began with a teahouse brawl between students and ruling party faithful at the edge of Rangoon and spread into marches to the center of the city.

Violent clashes took place over one week, during which, diplomats said, police brutality went far beyond the needs of crowd control. Male and female students alike were said to have been clubbed to the ground and savagely beaten. Some were reportedly beaten to death, and policemen were lynched.

The Government reported 2 dead and 140 arrested. People independent of the Government do not discredit a report circulated by Aung Gyi, a former associate of General Ne Win and now a dissident, that he knows of three police surgeons who said they had each performed 40 autopsies on riot victims.

During the March riots, much of the Rangoon public sided openly with the demonstrators. Many joined in marches, others gave shelter to students being chased by the police, and still others cheered the protesters from windows and balconies. Diplomats reported that police brutality, particularly toward women, was a major factor in turning sympathy in favor of the students. Protests on Campuses

Universities and schools were ordered closed. Reports suggest that in this period of enforced idleness an organized opposition movement was created among students and others. It became openly active when classes resumed May 30.

Protest meetings were held on campuses, during which students demanded the release of those in jail, the reinstatement of hundreds said to have been expelled and the right to form a student union.

The June 21 riot began with a meeting that led to a march downtown by perhaps 1,000 students. Once downtown, they were reportedly joined by many ordinary Burmese, including a significant number of Buddhist monks.

Diplomats, sensing a continuing air of what one called ''unfinished business,'' said the Government had reason to fear that July 19, commemorated as Martyrs' Day of the struggle for independence, may be the date of new anti-Government demonstrations.

Official Burmese newspapers were quoted as reporting today that five people were killed and an undetermined number were wounded during anti-Government protests over the weekend. Students in Rangoon, the capital, reportedly called for a nationwide general strike Monday.

The official Chinese press agency, reporting from Rangoon, quoted official Burmese newspapers as saying that the police opened fire Saturday to quell protests in three cities.

The reports said that protests in Pegu, 50 miles north of Rangoon, were broken up when the police opened fire, and that two people were killed and one wounded.

In Yenangyaung, in central Burma, one person was wounded when the police fired on 2,000 protesters who defied a ban on demonstrations, the reports said. The reports did not describe the other casualties or say what happened in Thanatpin, the third city where unrest was reported.

Burma named Attorney General Maung Maung, one of the Cabinet's two civilians, as the nation's new leader today, a week after widespread protests and violence forced his predecessor from office.

The first reports of reaction from Rangoon indicated that the people who have risen in protest remained unsatisfied and angry.

Diplomats in Rangoon said the selection of Mr. Maung Maung appeared to be an attempt to appease the protesters, who represent a broad cross section of the population and are calling for fundamental changes, including an end to 26 years of one-party rule.

But the diplomats said the students who led demonstrations last week, in which soldiers killed hundreds of people, issued a new call today for protests, including a strike similar to the one on Aug. 8 that touched off the violence. 'Things Have Gone Too Far Now'

''Things have gone too far now,'' said a Western diplomat reached by telephone in Rangoon. ''If all they're going to get is a shuffle of faces, the people have made it clear that this won't satisfy them.''

In a speech today reported by the official Burmese radio, the new leader did not directly address the main issues raised by the protesters. But he urged the ruling party to address the people's aspirations ''as soon as possible and as much as possible.''

''We need to review ourselves,'' he said, because it has become clear that ''consultation with the people has become weakened.''

Mr. Maung Maung is the third leader for Burma in the last month. On July 23, U Ne Win, who took power in a coup in March 1962, quit as leader of the Burma Socialist Program Party, citing a wave of protests that began in March. He was succeeded by U Sein Lwin, a former army general known for harsh suppression of dissent, but Mr. Sein Lwin resigned last Friday after a week of violent protests.

Mr. Maung Maung, 63 years old, was named President and leader of the nation's single party at a five-hour emergency session of the Parliament and party leadership today.

Some diplomats said Mr. Maung Maung, the fifth-ranking member of the Government, might have been chosen as a figurehead, with hard-line military men remaining in charge behind the scenes. Many diplomats say they believe Mr. Ne Win is still a power behind the Government. Member of the Ruling Clique

''They are seeking one of their own who might be acceptable to the people,'' one diplomat said.

The last week of Mr. Sein Lwin's 17-day tenure was marked by large, mostly peaceful demonstrations throughout the country that persisted despite shootings by the military. Hospital sources told diplomats they believed that more than 1,000 people were killed. Thousands more were arrested.

Mr. Maung Maung is a longtime associate and supporter of Mr. Ne Win, about whom he wrote a glowing biography, and is an author of the 1974 Constitution that enshrined the philosophies that have been so destructive to Burma.

Though the Government appeared to be making few concessions to the demonstrators, its radio station said a 10-man commission had been formed ''to study the economic, political and social wishes of the people.'' Question of Economic Revival

There was no indication that the one-party system would be changed, but the radio said ''qualified'' people who are not members of the ruling party could run for office.

In a half-hour speech to the 280-member party Central Committee that followed a brief address by Mr. Maung Maung, the deputy chairman of the Council of State, U Aye Ko, described at length economic changes begun by Mr. Ne Win before he left office.

These moves toward a more open economy do not appear to address the deep discontent and anger that have burst into the open around the country.

Mr. Maung Maung spoke in his address of plans for economic revival and said, ''If only the people had concentrated on these changes they would have been elated.''

A declaration by the nation's bar association this week listed seven demands, including creation of a multi-party system, an end to the state of emergency, the release of imprisoned students and Government critics, an end to the use of force against demonstrators, and an independent investigation and full disclosure of the casualties in recent killings.

Diplomats said Rangoon was tense and quiet today with a highly visible military presence.