A Senate staff investigation has produced no evidence to support allegations that elements of the US government have supported or acquiesced in right-wing ''death squad'' activity in El Salvador.
In a 36-page report resulting from the investigation, staff members conclude that in the course of carrying out legitimate United States government missions, some Americans have ''unavoidably'' had contact with Salvadoreans strongly suspected of being involved with death squads.
But the report, prepared by nearly a dozen staff members of the Senate Select Committee on Intelligence, says that the committee found ''ample evidence'' that US policy throughout the period under review (1979-1984) was ''consistently to oppose political violence in El Salvador.''
An Intelligence Committee member said that the staff looked at allegations contained in a Christian Science Monitor article of May 8 and found no evidence to support the article's contention that it is apparently with the knowledge of their US mentors that Salvadorean Army and intelligence units have tortured and killed Salvadorean citizens.
The Senate report was commissioned by the committee chairman, Republican Sen. Barry Goldwater of Arizona, following a request made in early April for an investigation of death-squad activity by Sen. Edward M. Kennedy of Massachusetts , a Democrat who has been critical of Reagan administration policies in El Salvador.
One of Senator Kennedy's main concerns was to determine whether the US Central Intelligence Agency was involved in any way in supporting death-squad activities.
Kennedy raised questions about a New York Times article that contained allegations from unnamed American officials that Col. Nicolas Carranza, former chief of the infamous Salvadorean Treasury police, had received more than $90, 000 a year from the CIA as an informant for the agency over the past five or six years. Committee members said that the Senate staff investigation found no evidence that this was the case.
One of the main sources for the Monitor article was a prominent Salvadorean civilian who requested anonymity. This source charged that American military advisers working with two departments of the Salvadorean armed forces' general staff and who were mainly Cuban-Americans, had to be aware of torture activities that were said to be common knowledge at the staff headquarters.
An Intelligence Committee member said that the just-completed staff investigation did not single out Cuban-Americans for special study. But he said that staff teams looked not only at CIA activities in El Salvador but also at those of the Department of Defense, including the Defense Intelligence Agency, the US Southern Command, and the National Security Agency.
The staff report is the first lengthy congressional study of death squads to be done to date, but it does not pretend to be the final word on the subject. The staff members limited themselves to interviewing US government personnel here and in El Salvador and studying US government material, much of it secret. They did not interview Salvadoreans believed to have information about death squads. They did read transcripts of interviews conducted by others with Salvadoreans concerned with the subject or knowledgeable about it, a key staff member said.
The House Committee on Intelligence is also preparing an investigative report on the subject of death squads which, one congressional source asserted, will ''go beyond'' the Senate study, because it will deal with the US training of Salvadorean security and intelligence personnel.
The Senate and House committees were created as oversight committees following congressional investigations in the 1970s which uncovered CIA abuses. One concern of liberal critics of the oversight system has been that the committees could become so involved in the intelligence process and ''mystique'' that they would be ''co-opted'' by the intelligence agencies. Two key staff members of the Senate committee are former CIA employees.
Senate staff members insist, however, that the just-completed report on ''Recent Political Violence in El Salvador'' is an independent study resulting from hundreds of man-hours of investigation by staff members appointed in equal numbers by Democratic and Republican senators.
Staff member Sam Bouchard said the unclassified, 36-page report was supported by ''several hundred pages'' of classified material. The classified material was available to any senator who wanted to look at it in a specially protected committee room known as a ''security cage,'' Mr. Bouchard said.
''Anyone who reads the classified material will realize that this is not a whitewash,'' said one staff member.
''I read the whole thing, and I saw nothing that provides any kind of corroboration of American involvement in death-squad activities,'' said Minnesota Sen. David Durenberger, a senior Republican member of the Senate Intelligence Committee. Eight Republicans and seven Democrats serve on the committee. The staff consists of more than 30 members.
Senator Durenberger said committee members as well as staff members had been ''burned'' by their lack of knowledge of the CIA-directed mining of Nicaraguan harbors last spring and wanted to restore their ''credibility'' by producing a solid report on the death squads.
Some committee members have not yet had a chance to study the classified material that backs up the new report.
Senator Kennedy, whose staff familiarized him with the unclassified public report, was campaigning for presidential candidate Walter Mondale in Texas when the report came out. Kennedy issued a preliminary statement saying that he was ''disappointed'' and ''shocked'' that the public report did not include detailed information as to what is known about the involvement of prominent Salvadoreans suspected of involvement in death-squad activities, such as the right-wing political leader, Maj. Roberto d'Aubuisson.
The public report said that the committee was not prepared at this time to discuss connections between named Salvadoreans and the death squads because: (1) intelligence reports on this subject do not involve eyewitness accounts of events or incorporate corroborating evidence of them and (2) disclosure of such information could actually make it more difficult to counter death-squad abuses.
Committee members said the Senate staff found no evidence that Salvadorean Treasury Police chief Carranza had received anything like the $90,000 yearly that the New York Times reported in March. But the public portion of the Senate report does say that Carranza ''had official contact with the US government at various times.''
''The committee is concerned that through its maintenance of contact with Carranza the US government may have been perceived to be associated somehow with the political far right in El Salvador,'' the report says. ''There is little evidence, however, to indicate that Carranza was personally involved in extreme right-wing political violence. The committee has therefore concluded that the US government did not become implicated in political violence through its contact with Carranza.''
The Monitor story of May 8 said, however, that sources in the Senate Intelligence Committee, the CIA, and the State Department confirmed the New York Times's report.
Carranza himself had denied the allegations that he was on the CIA payroll or involved in death-squad activity. Carranza was recently assigned to a diplomatic mission overseas.