Frank Gannon is emerging from self-imposed seclusion, coming back to Washington after three years behind the walls of San Clemente where he became perhaps the closest non-family member to Richard Nixon during the months the former president spent writing his life story.

"I think he understood his book had to be very candid in character," says Gannon, "but writing it was... an intellectually uncongenial process. He doesn't like the backward-looking discipline of writing an autobiography."

Gannon should know. Now 36, he was chief researcher for Nixon's book RN , published last year. Gannon says he got $42,000 a year from Nixon to assist in the organizing, researching and editing of the manuscript, a manuscript for which Warner Paperback Library is said to have advanced $2 million.

For Gannon -- a historian by training -- working on the book offered an insider's look at Nixon. At the same time his participation produced puzzled reactions from friends who couldn't understand how the young, liberal Republican Gannon -- a lover of rock music and avant-garde comedians, a man who in his college days at Georgetown played show tunes at the piano at President Kennedy's parties -- could hitch his wagon to a disgraced president.

But after Gannon finished his work on RN , he had little trouble returning to Washington politics; last month he began work as the top man in the office of Sen. John Heinz (R-Pa.). As the wealthy and ambitious lawmaker's administrative assistant, Gannon says he wants to help his boss "cast a very wide informational net" by bringing him together with experts on issues the he might want to pursue.

Yet Gannon will always be remembered as the person who shared Richard Nixon's years of exile.

"The first six months [after Nixon resigned], I was on the transition team," recalls Gannon, who says former White House press secretary Ron Ziegler handled Nixon's end of the book contract negotiations. "For the first year, I don't know, I guess I was younger then, I'd drive to LA two or three nights a week to the Roxy or the Troubadour or the Orange Julius on Santa Monica."

Then the pace quickened, and in the last year and a half of working on RN, Gannon says he didn't leave San Clemente more than six times. He felt some pressure, he says, because sometimes there were only three or four months to research a chapter that might cover 10 years of Nixon's life.

Nixon would do what his staff called "dictations" based on the "information packets" provided by Gannon and an assistant. Those dictation tapes -- the sum of which contained 800,000 to 1 million words -- were then transcribed by temporary secretaries who were asked to sign an oath not to reveal what they learned during their tour of duty at the Nixon compound.

"He maintained such complete seclusion, there was very little press pressure and presence," says Gannon. He remembers Nixon pushing to complete the book in the face of his wife's illness, his own phlebitis and adverse court decisions regarding his presidential papers. Even the news stories that accompanied publication of The Final Days, with its sometimes harsh portrayal of the Nixons, did not seem to affect Gannon's boss. ("He hasn't read The Final Days," says Gannon. "He said he was unconcerned, but I don't think he really was.")

Gannon was familiar with books by historical figures. The son of a Long Island building supply salesman, Gannon went to work with Randolph Churchill while pursuing his D.Phil. in political science at Oxford University. (His master's is in international relations from the London School of Economics; his bachelor's is in foreign service from Georgetown.) Gannon was one of Churchill's "young gentlemen" who assisted in the preparation of Randolph's history of his father, Winston.

"I thought of myself as an academician," says Gannon, who returned to the United States to look for academic jobs until he "found I was a glut on a small market."

He wound up hiring on as a speechwriter for the head of the giant ad agency, J. Walter Thompson. It was that job he left to become a White House Fellow in the summer of 1971.

He was asked to stay on at the White House as a memo and speechwriter to the head of the White House domestic council. But as the clouds of Watergate began to gather, Gannon grew dissatisfied with his blurry job description and the way the admnistration's energy was diffused by the scandal. His first meeting with Nixon occurred as he prepared to quit the White House.

It was traditional for departing staffers to have their photo taken with the president, and when Gannon visited Nixon in his office to say farewell, Nixon asked him to consider staying. Gannon did, and wound up going to San Clemente with Nixon.

When asked, Gannon will tell strangers what he has been doing the last several years. Sometimes he is not believed, but inevitably people remain curious. Gannon kept notes about his time at San Clemente, though he says he wouldn't consider writing about the experience while Nixon is still alive. And he's disappointed that reviewers, he says, wrote their opinions about Nixon instead of the book.

"There was so much new material," Gannon says. "I think that it's a book whose time -- though it filled its commercial expectations -- has not yet come."