El Salvador's 80-day coalition government collapsed yesterday as the two most liberal members of a five-man junta and nearly the entire cabinet resigned, charging the armed forces had failed to allow promised political and economic reforms.

As announcements of the mass resignation of at least 37 high-level officials were made throughout the day, leftist guerrillas seized six key radio stations and broadcast pledges that 1980 would be a year of violence against what remains of the government.

Among those resigning yesterday were junta members Guillermo Ungo, head of the social democratic Nationl Revolutionary Movement and Catholic university rector Roman Mayorga. Remaining in the junta are moderate businessman Mario Andino and two Army colonels who headed an October coup that ousted rightist president Carlos Humberto Romero.

The streets of San Salvador, the capital of the Central American nation of 5 million people, were reported calm last night, with no statement from either the military or remaining government civilians on the situation.

"Everyone is just waiting nervously," said one informed source contacted by telephone in San Salvador. "We know something is coming, but we don't know what or from where."

The coalition was formed Oct. 15, when young military officers joined with left-center civilians in a government that pledged to end political repression and economic inequality.

While leftist militants who had been battling the Romero government originally called a truce with the new regime, violence has sharply escalated again over the past month as promises of reform were not fulfilled.

The leftists charged that demands for increased salaries were unmet, an agrarian reform program was not implemented and, most importantly, military and police officials accused of repression and human rights abuses were neither removed from their positions nor punished.

Civilians who joined the new government, primarily liberal politicans from major opposition groups under Romero who hoped to stem the growing popularity of the extreme left, found their own popular credibility falling as it became clear the more moderate members of the military were either unwilling or unable to make good on their promises.

The resignatiions began Tuesday evening when the National Democratic Union, a communist-backed political party, withdrew five of its members from government positions. On Wednesday, several minor Cabinet ministers resigned, followed yesterday by Mayorga, Ungo and all members of his party in the governmnet and all members of the leading Christian Democratic Party.

Among the Christian Democrats were foreign minister Hector Dada and Ruben Zamora, the chief of staff of the junta. One source in San Salvador said only Defense Minister Col. Jose Guillermo Garcia remained of the junta's cabinet.

The original appointment of Garcia -- who had been in charge of a military unit under Romero charged with human rights abuses -- as defense minister had been strongly protested by both leftists and moderates.

In a signed statement released yesterday, a number of resigning cabinet ministers and agency heads charged the military with failing to "concretely begin a process of democratization and the necessary structural reforms."

In presenting their "irrevocable resignations," the signatories criticized the "inclusion in the present government of reactionary forces who are tied in their very roots to the big [economic] oligarchy [and] the failure to achieve closer ties with popular movements whose existence and importance can no longer be ignored in El Salvador."

As a result, they said, the armed forces have turned "to the right and in retarding the initiated the process of change and democratization begun to endanger all the objectives" that brought them into the government in the first place.