Every administration has its political purges, so it wasn't earth-shaking news when the Reagan administration, shortly after taking office, created a sort of exile status for some Democrats it couldn't ease out of the Agriculture Department.

The "boneyard" is what this gulag of nullity was jokingly called around the department, and that is where a man with the improbable name of Chipman C. (Chip) Bull went to repose in 1981.

Now, bankrolled with nearly a year's worth of accumulated leave pay, he has left the USDA and is running for Congress in his home district in Maine, against Republican Rep. Olympia Snowe.

Here is how Bull advanced from the boneyard to a congressional race:

Bull, an unflinching Democrat, went to work for the Agricultural Stabilization and Conservation Service (ASCS) in 1957 as a temporary worker in Maine. By 1968, he was the state director--a political job--but when Richard Nixon won the presidency that year, Bull knew his days were numbered and he quit.

He became an executive of the Maine Potato Commission. In 1976 Democrats recaptured the White House, and the Carter administration made him the Northeast area director of the ASCS, overseeing federal farm programs in 13 states.

Bull became a "career" employe in 1979, joining the Senior Executive Service. Naively or not, he thought that in 1981 the new Republican team would put his talents to work in running the USDA. They did, but only briefly.

Little by little, by Bull's account, his duties were taken away and he finally was dispatched to the boneyard--a highly paid bureaucrat with nothing, absolutely nothing, to do.

He says he got so adept at solving The Washington Post's crossword puzzle each day that it became a bore. He moved on to the more complex New York Times puzzle and got it down to a 20-minute exercise. He felt badly when The Evening Star folded because its puzzle had helped him while away the afternoon.

When he wasn't working puzzles or drinking coffee in the cafeteria, Bull did a lot of reading. He read all of the Ludlum thriller novels. He read Leon Uris' "Trinity" and liked it so much that he read it a second time. He also thought highly of "Exodus," another Uris book that he polished off on the job.

Maybe that was bad enough, paying a man $50,000 a year to read novels and work puzzles. But when his Senior Executive Service salary went overnight from $50,000 to $58,000, Bull was upset. "That really incensed me," he said. "It was at a time when federal programs were being cut back and they were trumpeting about all the waste, fraud and abuse they were eliminating."

Nonetheless, Bull stayed on--it was the only job he had and he figured he was there to work even if his superiors wouldn't let him. One of his former supervisors said, "From what little I knew, he was a good employe, but he wasn't interested in a transfer and he decided to opt out."

Bull put it this way: "I was upset . . . . Here I was, 48 years old with more than 20 years' experience, and then I was relegated to the bone pile without a nod. I felt it deeply, . . . lost confidence in myself, felt I was a hack. And my home life suffered. So around February I decided to leave, and on March 5 I was gone."

Then, because he had little to do and cronies were nagging him to become a candidate, he decided to run for a House seat. "People asked why would I want a job that pays only $5,000 more than what I was making at USDA," he said. "Well, I feel things can be done in the legislative branch, and I think I know where the skeletons are at USDA. I intend to be on the Agriculture Committee."

It might have started as a semi-lark, but Bull's race has become a serious matter. Friends at the Democratic National Committee are coaching him. Sen. George J. Mitchell (D-Maine) and his predecessor, Edmund S. Muskie, are promoting his candidacy, and he has mounted several fund-raising efforts here.

His campaign slogan may say it all: "It's Bull." CAPTION: Picture, Chipman C. Bull, $58,000-a-year man, says, "I know where the skeletons are at USDA." By Ray Lustig--The Washington Post