A. Ernest Fitgerald has been a bigger burr under more Washington saddles and for a longer time than any federal civil servant in memory. He has tormented and caused turmoil for five presidents, plus White House aides, Pentagon leaders and other officials over a 13-year period.

"I said get rid of that son of a bitch," Richard Nixon said in a taped White House conversation in 1970. The former president thus managed to get himself sued and, it now turns out, extricated himself by secretly paying Fitzgerald $144,000 in damages. He may have to pay him $34,000 more.

Nixon had tried hard to avoid such a result. In a sworn statement to Fitzgerald's lawyers in October, 1979, a few months before making the payment, he praised Fitzgerald as a "cost-cutter" who might make an "ideal" director of the Office of Management and Budget. He went on to offer "to intercede privately, on a very private basis, off-the-record basis, with President Carter."

Now 55, the feisty, individualistic Fitzgerald has been known as the government's No. 1 "whistleblower" since November, 1968, when he told a Senate hearing of a $2 billion overrun in the Lockheed C5A cargo plane program. A decade later, President Carter credited him with the inclusion of whistleblower provisions in the 1978 civil service reform law.

But Fitzgerald cares little for Carter, under whose administration he spent four years in Pentagon limbo; doesn't want credit for the provisions of the new law, which he rates a failure, and dislikes the term whistleblower.

It may put a "stool-pigeon taint" on persons who tell the truth to Congress, "which is what they are supposed to do," he once said. "The problem is with the folks who don't tell the truth."

Fitzgerald hasn't been heard to praise President Reagan, either. His new Pentagon and Air Force chiefs have spurned his offers to help cut costs. They have extended his lease on limbo on a month-to-month basis while trying to cope with a federal judge's order that he be restored to his former GS17 post as Air Force deputy for management systems or equivalent status.

In addition, the administration has promoted Lt. Gen. Hans H. Driessnack from comptroller to assistant vice chief of staff of the Air Force, its third-ranking position. He had been named by Fitzgerald as one of several officials who had conspired to have him fired, including Nixon, White House aides H.R. Haldeman and Bryce Harlow, and then-defense secretary Melvin R. Laird.

Driessnack has sworn that had "absolutely no connection with any effort to terminate Fitzgerald's position."

The 1968 cost overrun disclosure, at the end of the Johnson administration, offended then-Air Force secretary Harold Brown. In a memo following the transition meeeting with his successor under Nixon, Robert C. Seamans Jr., Brown accused Fitzgerald of "unacceptable" practices, such as "discussing internal Air Force matters" on Capitol Hill.

He wrote that he did not yet have "sufficient reason" to fire Fitzgerald. But he wrote that Seamans agreed Fitzgerald "is of no use to the Air Force" and "is to be discouraged from remaining."

In November, 1969, Fitzgerald was told his job was being abolished for economy reasons, but Laird admitted two weeks later that he had been "fired." Fitzgerald left the Pentagon but began a long and successful return march, to the limbo where he had no key responsibilities, via administrative and court challenges.

Seamans and other officials invoked presidential executive privilege to avoid answering questions about the White House role. Nixon approved this.

In the 1979 deposition, he swore he had fired Fitzgerald in the mistaken belief that he was firing Gordon W. Rule, a civilian Navy procurement expert "who had been publicly attacking" Roy Ash, his nominee to head the OMB.