American church leaders have mounted a determined campaign to block $5.7 million in U.S. military aid to the present government of El Salvador.

In the wake of the recent assassination of Archbishop Oscar Romero, Protestant and Roman Catholic church leaders here have taken up his call for an end to American aid to the ruling junta in that country.

More than a month ago, Romero, who had been El Salvador's leading spokesman for peaceful change, wrote a letter to President Carter, appealing to him as a fellow Christian not to send more military aid to the strife-torn country.

Because the official response to Romero's appeal was deemed "less than adequate" by some religious leaders in this country, the National Council of Churches and the American Friends Service Committee joined U.S. Catholic forces in sending a fact-finding team to El Salvador.

The team, which was in San Salvador, the capital city, when the archbishop was murdered, returned last week, determined to block U.S. aid to El Salvador.

Ronald Young, the American Friends representative said, "Whatever our intentions (in making the grant of military aid funds), it would be perceived by the Salvadorians as support for the repression" by the current regime.

Archbishop John R. Quinn of San Francisco, president of the American Catholic hierarchy, pressed the issue with President Carter when Carter made a condolence call after Romero was slain.

"I thanked him (Carter) for his expressions of sympathy," Quinn recalled, "but I took advantage of the conversation to say that we are now even more conscious of the letter Archbishop Romero had written him and that we hoped he would reconsider his answer."

Earlier this week, as House and Senate subcommittees considered aid to El Salvador, bishops and other church leaders from around the country urged key members of Congress to oppose it.

The aid funds have already been appropriated, but House and Senate appropriations subcommittees on foreign operations have been interested in giving it a second look.

Despite pressure from church groups, the House subcommittee approved the aid Tuesday by a 6-to-3 vote. The Senate subcommittee, however, has filed an objection.

Church leaders object to the aid because they contend El Salvador's present government is even more violent and repressive than the regime of Gen. Carlos Humberto Romero (no relation of the archbiship), which was overthrown last Oct. 15.

The church leaders who visited El Salvador last week, all of them long-time experts of Latin American affairs, said they were "particularly shocked by the barbarity of the repression" they learned of there.

"We have heard testimony from eyewitnesses or rape, torture, mutilation, decapitation, garrotting and the murder of unarmed and defenseless men, women and children," they said in a report of their findings.

The fact-finding team said that in the first 2 1/2 months of the present regime, 682 persons were killed, 211 detained and 176 have "disappeared," figures that they said "far exceed those of the entire three-year regime of Gen. Romero.

Church leaders took issue with reports from the U.S. ambassador and the ruling junta that leftists bear much of the responsibility for the killings. The visiting church leaders said they found extensive evidence of killings and other atrocities carried out by members of the military forces, often in uniform, who moved into villages and chose their victims from prepared lists. The lists, they charged, are drawn up with the collaboration of ORDEN, a right-wing paramilitary group, which the church leaders charged, controls portions of El Salvador's military and police forces.

The Rev. Alan McCoy, a Catholic member of the American fact-finding team, pointed out that under the present regime, there have been 8 1/2 times as many leftists killed as ordinary citizens.

In the same vein, a group of 22 Latin American bishops attending last Sunday's funeral for Archbishop Romero challenged the government's attempts to blame left-wing groups for the violence that erupted at the funeral and left at least 30 dead.

Archbishop Quinn, who represented the U.S. church at the funeral, took a similar position.

"It has been said that the leftists were responsible [for the violence at the funeral]," he said in a telephone interview after his return from El Salvador, "but I find that very hard to believe."

Quinn added that the first bomb that erupted at the funeral "seemed to be aimed at the [leftists]." Furthermore, "the crowd at the funeral seemed to be mostly peasants -- not members of the oligarchy. It's not that I want to defend the leftists, but I find it very difficult to believe that the leftists would throw bombs at these people," he said.

Quinn said that the government security forces "as far as I could see, certainly did little or nothing to restore order or restrain the crowds" at the funeral, once the bombs and gunfire had erupted.