The FBI conducted a six-year investigation into possible terrorist links and activities by hundreds of individuals and organizations that have opposed the Reagan administration's policies in Central America, according to bureau documents released yesterday by a New York civil rights group.

The documents indicate that the FBI's investigation of the Committee in Solidarity with the People of El Salvador (CISPES) extended from 1981 through 1987 under former director William H. Webster and involved massive use of surveillance, informants and undercover agents.

The Federal Bureau of Investigation started probing the CISPES, then branched to include other church, labor and civil rights organizations, the documents show.

CISPES said today that other groups named in the documents included the Southern Christian Leadership Conference, the Friends Religious Society, the American Indian Movement, the Maryknoll Sisters, Witness for Peace, the United Steel Workers and United Auto Workers, the National Education Association, the Tallahassee Peace Coalition and several campus student groups.

A sampling of the documents were released by Margaret Ratner, an attorney for the Center for Constitutional Rights, based in New York. They showed that the FBI conducted surveillance of meetings, took down names of participants in them, recorded license plate numbers and the like, but there was no evidence in the documents released of more aggressive forms of surveillance. One wiretap was referred to, but it may have been part of a separate case, and was authorized by a court.

Ratner said that, by conducting the investigation as a terrorism inquiry, the FBI was able to use intrusive investigative techniques that would be considered illegal under guidelines for domestic investigations.

Ratner said individuals and groups affiliated with the CISPES have been plagued by a series of break-ins, burglaries and incidents of vandalism. She compared the FBI's behavior in the current investigation to its activities in the 1960s and early 1970s when the FBI conducted so-called "black bag jobs" against antiwar activists.

Questioned further, she said the CISPES has no evidence linking the incidents to the FBI.

Ratner said the center obtained about 1,200 pages of investigative documents, many of them heavily blacked out, through a lawsuit under the Freedom of Information Act. She said the FBI has refused to produce 2,400 pages of related documents.

"The investigation amounted to a wholesale collection of information about the lawful political activities of those who opposed U.S. policy in El Salvador," said Jerry Berman of the American Civil Liberties Union. "The files are . . . about peace demonstrations, political organizations and campus politics."

FBI spokesman Lane Bonner said he cannot answer specific questions about the CISPES investigation because much of the information is classified and part of ongoing lawsuits.

"The FBI is responsible for domestic security/counterterrorism investigations in the United States," Bonner said. "These investigations are conducted pursuant to U.S. laws and attorney general's guidelines . . . . "

In one secret 1984 communication from FBI headquarters to the Pittsburgh field office, the bureau identified the CISPES as a "national organization involved in communist activities supporting communist insurgents in El Salvador . . . . "

It said the group's leadership "covertly furnishes . . . funds and materials to the guerrillas in El Salvador, assists in the maintenance of camps in the United States for the rehabilitation and reindoctrination of Salvadoran guerrillas . . . either to be returned to the fighting in El Salvador or to remain in the U.S. to establish guerrilla cells."

It added that the FBI wanted to investigate smuggling of illegal aliens and "potential for violent demonstrations in the Pittsburgh area . . . and the extent that these and other clandestine activities are intended to aid foreign terrorists."

In a memo dated July 27, 1984, Webster wrote that "many of the people and groups involved with CISPES . . . are not aware of or involved in the CISPES covert activities . . . . "

"It is imperative that these investigations are closely supervised and monitored to ensure our investigations do not infringe upon the rights of these individuals or groups protected by the constitution," the memo said.

In several communications, field offices warned that they could not produce enough evidence of wrongdoing or suspicious activities to justify a terrorism investigation.

Angela Sanbrano, a CISPES member, said her group is involved in "building protests, demonstrations, congressional pressure, educational events . . . raising humanitarian aid for civilian projects and response to human rights violations . . . . "