Jessie L. Gill said yesterday she is planning to write a book about her experiences as an FBI and CIA informant. Such a volume would be revealing, for reporters in the Boston area have been chasing around the past two days to check the many aspects of her story that strain credulity.

The only official comment on the case thus far was a curt acknowledgement Monday by an assistant special agent in the FBI's Boston office, Vincent H. Rueul, that Gill had indeed worked for the Bureau in the late 1960s.

FBI Spokesman

Rueul at that time refused to discuss the case further, and since then neither he nor any other FBI or Central Intelligence Agency officials have spoken out on the case.

Nonetheless, certain features of her story about her three undercover years, during which she fed information to the FBI and, she claims, the CIA, while she was active in Harvard SDS, are beginning to ring true.

Dean Whitlock recollected Tuesday that the FBI had called him in the summer of 1969 and informed him that a secretary he had hired for the summer was a member of SDS. Whitlock, who was then an assistant to President Nathan M. Pusey '28 for civic affairs, verified that the woman was indeed a member of SDS. "I always wondered how the FBI found out," Whitlock said.

Gill, who knew Whitlock at the time, yesterday supplied the answer. "I told the FBI that woman was working for Charlie Whitlock," she said.

Gill also claimed yesterday to have spoken about her activities with a Time magazine reporter last summer. The reporter, Edward Magnuson from the magazine's New York bureau, yesterday verified her story.

"I talked to Jessie Gill in New Hampshire in the summer of 1972," he said. "She was hard to evaluate, but I had no reason to doubt much of what she was saying."

Gill's claims are indeed hard to evaluate, even for a veteran reporter like Magnuson, a man who has followed the intelligence world for years. Some of her statements seem outrageously outlandish, but the FBI settled a basic question Monday when it admitted she had been on its payroll.

Still, other points in her growing story, especially her allegations concerning the Central Intelligence Agency, remain to be proven. She said two CIA men, including Herman A. Mountain, chairman of the agency's Cambridge Bureau, paid her $350 for telephone expenses at a March 3, 1972, rendezvous in North Conway, N.H.

Verification of this claim, and of her additional allegations that she supplied the CIA with a steady stream of information at the same time she was working for the FBI, can only come from the still-silent CIA or a knowledgeable third source.

Gill said she approached the FBI in February 1967 through friends in the CIA. Although she favors social change, she said, she objected to what she called the violent, unpatriotic attitudes of Harvard SDS members.

"I didn't like people coming up to me on the street and tearing down the country," she said. "I made my decision to go to the FBI, but then I went home and shook for a few hours afterward."

Gill said she was in regular communication with both intelligence agencies, although she refused to specify either the names of her contacts, how they were reached, what type of information she transmitted, or how much she was paid, other than that "it was under the minimum wage."

Gill did claim she called the CIA headquarters in Langley, Va., 18 hours before the 1969 SDS-led University Hall occupation, "to warn the Agency." She said the CIA took no action because of administrative foul-ups.

She said she attended national actions for the FBI, although she declined to specify her role in them. She did explain that the FBI warned her to avoid militant confrontations. "They told me to avoid violence or serious trouble," she said.

Gill stresses that she worked with--not for--the FBI. She said she helped them because she feared SDS was a threat to national and local security, "but I always tried to do all I could for the poor."

"I legitimately represented the interests of the 64 families in my Mount Auburn St. apartment building," she said.

Gill said her desire to help the poor at times conflicted with her intelligence work. "I walked a razor's edge for four years," she said.

Gill complained about what she called the poor pay and lack of training in intelligence work. "They send youngsters into the field who don't know anything," she said. "That's why most informers only last for two to six months."

Gill seems to have a special vendetta against the CIA and its Cambridge chief, Herman A. Mountain, whom she claimed she knows. When informed that Mountain had refused comment on the case, she responded, "Herman's scared. He's nothing but a pussy-cat."

Those who knew Gill in her Cambridge days seriously question her credibility. They say she was considered "a lunatic" then and doubt her ability to perform skillful undercover work rationally.

Arthur C. Egan, chief investigative reporter for William Loeb's Manchester N.H., Union-Leader, agrees. He said Tuesday Gill was "extremely neurotic" and that she always feared for her life.

Coming from a correspondent from a conservative newspaper likely to grant Gill more than a perfunctory hearing, Egan's assessment is particularly telling.

Still, although perhaps many of Gill's allegations should be taken with a healthy dose of salt, her role with the FBI at least is unmistakably true. And until contrary evidence appears, much of the rest of her story will have to be weighed seriously.

"I'm completely independent," Gill said yesterday. "Neither Harvard, MIT, the FBI nor the CIA could comprehend me.