JESSIE L. GILL was picketing outside Holyoke Center in January 1967, protesting what she termed unsatisfactory conditions in her Harvard-owned Mt. Auburn St. apartment building.

Members of the growing chapter of Harvard SDS approached her, she said, and offered their support. "I got frightened by those SDS kids," she said. "I didn't like people coming up to me on the street and tearing down the country. I decided to work for the FBI, but I went home and shook for a few hours afterward."

Gill said she contacted a friend of hers who was active in intelligence work in World War II. "He put me in touch with someone he knew in the CIA, and they referred me to the FBI," she said.

Gill thus inaugurated a three-year career as an informer, during which she says she funneled the names of "thousands" of radicals to the FBI. She also moonlighted for the CIA, she says, keeping the agency informed of the activities of area activists so it could protect its Technology Square office.

Gill says her relations with the two intelligence agencies were never idyllic--"I was paid one-third under the minimum wage by the FBI"--but they steadily worsened. She had a final falling out with the FBI in 1970, and the bureau "moved" her to New Hampshire, where she now quietly attends school, works in a local hospital, and is planning to write a book about her undercover experiences.

"If anyone comes to bother me here my neighbors will start shooting," she said. Gill is openly and sharply critical of the two intelligence agencies and appears willing to spill gradually what she knows about their operations. She apparently feels no shivers at coming in from the cold.

During her career underground, she came in contact with a wildly disparate set of personalities. The late J. Edgar Hoover, Harvard SDS leadership, conservative publisher William Loeb, Rep. James C. Cleveland R-N.H.) and Dean Whitlock all dealt with her in some way.

Whitlock and the SDSers knew her only as a bizarre butvocal critic of Harvard's housing policies in Cambridge, particularly in her own building, Hoover, Loeb and Cleveland came into the picture in 1972, when Gill attempted to get her back pay for telephone expenses she incurred during her shadowy career.

Certain aspects of her story strain credulity, primarily because neither intelligence agency has discussed Gill's work, other than the FBI's curt acknowledgement that she indeed informed for them. Gill herself, however, is part of the problem.

Thus far, Gill described her undercover work only in the vaguest sort of terms, although several bits of specific information she has provided have checked out.

She has refused to go into her methods of operation, what type of information she made available to the intelligence agencies, how or to whom she passed the information, or how much she was paid, other than that her salary was "under the minimum wage."

Gill has acknowledge, however, that she told the FBI that a woman secretary employed by Dean Whitlock was an SDS member, and she accurately located the Cambridge CIA office at 545 Technology Square.

Whitlock said the FBI called him unexpectedly in the summer of 1969 to warn him about his secretary. "I always wondered how the FBI found out" Whitlock said.

Three Crimson reporters verified Gill's tip about the CIA office. The agency maintains spartan quarters in Room 304 at the Technology Square address. No identifying insignia other than the room number were on the agency door or anywhere else in the office.

Gill said the CIA wanted to be kept abreast of the activities of Cambridge radicals because it feared for the safety of its office, which is indeed located in an area with a high incidence of militant demonstrations. Had the agency's location been public knowledge, bricks would undoubtedly have been heaved through its windows frequently in the past few years.