Two subcommittees of the House International Relations Committee heard evidence yesterday of massive fraud in presidential elections last month in the Central American republic of El Salvador.

A large audience including many Spanish-speaking State Department officials and human rights activits, listened with astonishment to a tape recording of broadcasts by El Salvador's ruling party on the Feb. 20 election day referring to "stufing tamales in the tanks."

That means "stuffing fraudulent votes in the ballot boxes," explained William Brown of the Washington Office on Latin America - a coalition of church and human rights group that presented the taped broadcasts as evidence of what he called "massive fraud."

The hearing chaired by Reps. Donald M. Fraser (D-Minn.) and Gus Yatron (D-Pa.) was called to consider cutting off U.S. aid if it is found that Salvadorans's human rights were violated.

Committee staff members said there is no known precedent for a U.S. congressional investigations into another country's election.

Fraser, an early activist in the burgeoning U.S. concern with human rights, declared that "the right to vote and to have free and genuine elections is a basic huma right." He cited evidence including the tapes presented to the hearing as showing fraud occured in the Feb. 2 election won by the military-backed ruling party's candidate, Gen. Carlos Humberto Romero.

"Our subcommittee are not seeking to tell the El Salvadoran government how to run their elections," he said, but "the right of free elections . . . should play a role in determining U.S. foreign policy - and particularly U.S. assistance programs."

Brown said that the evidence, including the tapes, was gathered by the Christian Democrats of America, an international organization of Christian Democratic political parties, which sent an observer to the Feb. 20 vote. He asked for "an expression of concern on the part of officials in the present administration" and a cutoff of military aid to El Salvador.

Deputy Assistant Secretary of State Charles W. Bray III testified that while human rights violations occur in El Salvador, they have not formed a consistent pattern to justify cutting off aid, which he said is under $10 million.

Bray refused to testify in public on whether or not the voting was fradulent. He said it was not possible in any event to say if fair elections would have changed the results. The official margin was almost 2-to-1 for Gen. Romero over retired Col. Ernesto Antonio Claramount, a Christian Democrat who was forced into exile in Costa Rica after his followers protested the results.