The bodies of three nuns and a lay woman, all Americans, were exhumed from a roadside grave today 36 hours after they were reported missing. Three had been shot in the head and one in the chest, and at least two apparently had been raped.

Diplomats and Salvadoran officials said they believed the killings of the women, who sought to work with the poor here, were part of an extreme rightist plot to seize the government and eliminate Roman Catholic efforts at reform.

Nuns Ita Ford, 40, and Maura Clarke, 46, of the Maryknoll order, and Ursulan Dorothy Kazel, 40, and lay worker Jean Donovan, 27, apparently were killed Tuesday evening. Kazel and Donovan were from Cleveland and the other two from New York.

The initially unidentified bodies were found Wednesday morning about 30 miles from the capital and hastily buried by local officials who dug a single grave in a cow pasture.

They were exhumed today and identified by friends, including U.S. Ambassador Robert White, who was quoted by a reporter at the scene as saying, "This time they won't get away with it. They just won't." Later, White refused further comment. Judicial officials at the scene said at least two appeared to have been sexually molested.

Coworkers said Kazel and Donovan were in a group of church people who dined with White Monday and stayed at the U.S. residence that night.

The killings, some diplomats and officials fear, could be a final blow to the U.S.-backed colition of military and civilians that rule this beleaguered Central American nation. Within the last several days selective, brutal terror has increased at a politically dangerous rate -- this in a population of 4.8 million that has seen more than 9,000 political leaders were assassinated, precipitating the most serious crisis yet for the fragile government that barely survived its first year in power confronted by a growing guerrilla movement and the extreme right's terrorism.

The Catholic Church has been intimately involved with the struggle for reform here since many of its priests began openly advocating a restructuring of this near-feudal society in the 1970s and more recently accused the government of wanton repression. As a result, clergy have become the focus of a concerted campaign by rightist death squads, sometimes allegedly working with elements of the armed forces.

Nine priests have been killed in recent years. Last March, archbishop Oscar A. Romero, who had become a major political figure and advocate of human rights, was gunned down as he celebrated an evening mass.

In the last week, two more Salvadoran priests, Marcial Serrano and Ernesto Abrigo, disappeared under mysterious circumstances. The government has failed to bring any of the priests' killers to justice, or even to identify them.

Tonight Christian Democratic junta members Napoleon Duarte and Jose Antonio Morales Ehrlich, along with two Cabinet members, called a press conference and denied categorically that the government is persecuting the church.

Duarte said that in his opinion the nuns were killed by right-wing extremists as part of a series of "strategic crimes" designed to further destabilize El Salvador and overthrow the current junta.

The government spokesman announced the junta ordered an immediate investigation of the "abominable" crime. Duarte did not rule out the possibility that some elements of the military or the government "might have been involved" in the death of the women.

At the same time, right-wing commentators speculated that the killings could have been perpetrated by the leftist guerrillas to embarrass the extreme right. No group immediatedly claimed responsibility.

One senior Catholic official said, "This killing is simply horrendous, going beyond any limit any kind of action we've seen before. We know where these things come from but it is dangerous to say so."

The four initially were reported missing after a van was discovered burned-out and empty yesterday morning. It had been used by Kazel and Donovan to pick up the Maryknolls from the national airport, about 40 miles south of the capital.

[the Maryknoll Order issued a statement from its New York headquarters, saying "evidence provided by reliable sources close to the situation indicates that the military was instrumental in the disappearance and death of these four women."]

The murder of the American nuns is expected to complicate the task of U.S. policymakers -- both of the current and incoming administrations.

The opposition, as well as international human-rights organizations and political groups in a number of countries, have charged that the goals and the methods of the junta and the extreme right are the same and that they include the same people in many instances.

[Amnesty International, the London-based human rights organization, said it had sent messages to the United Nations "pointing to the overwhelming evidence that Salvadoran troops were responsible for the detention and murder" of the opposition leaders.]

Previously, military training had included instruction on how to recognize "subversive" priests by the length of their hair, their adoption of civilian dress and their close relationships with the youth in their communities.

Although the United States has conducted military training with a "human rights component" for noncommissioned officers, many soldiers and officers still believe that the church is harboring subversives and contributing to the strength of the left here.