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."