J. Hamilton Lambert, the Fairfax County executive for 10 years, is sometimes referred to as the dean of the Beltway bureaucrats. He has mediated regional squabbles, amassed extraordinary power and outlasted all his peers in the Washington area.

Now, sources close to Lambert say, he is increasingly disenchanted with his job and is seriously considering retiring.

The sources cite, among other reasons, the strain on Lambert of working for a fractious Board of Supervisors; his deteriorating health; a large pension he could receive starting in November; more frequent public attacks and calls for his resignation; lucrative job opportunities; and the possibility he could become a campaign issue next year, when all nine board seats will be up for election.

"There's been a lot of speculation about what I'm going to do, whether I'll leave at the end of this year or stay through this board" term, Lambert said in an interview. "Right now, I have made no definite plans."

Lambert said he has received "five to 10 job offers" in the last year, in both the public and private sectors, adding, "I have neither solicited them or discussed them in any great depth."

At least two issues could affect Lambert's decision, according to close associates. One is his desire to leave county service on a high note, rather than appearing to have been hounded from his job. He started with Fairfax County in 1959 as an assistant map draftsman and climbed rapidly through the ranks to become its chief administrative officer in 1980.

The other issue is a sense of loyality to the board. Lambert is the county's leading budget expert, and with taxes likely to play a key role in board elections next year, he could help the supervisors craft a leaner budget with deeper tax cuts.

What is focusing attention on Lambert's possible retirement is his eligibility for generous benefits. When he turns 50 on Nov. 18, Lambert could retire and collect an annual pension of $72,000.

Health considerations also are a factor, according to associates. Lambert, who is overweight and smokes almost three packs of cigarettes a day, recently underwent a battery of medical tests that he told a confidant had thoroughly "humiliated" him. The result: He is on a liquid diet and has dropped more than 20 pounds in three weeks. "That's one of a number of things I'm doing as a result of medical advice," he said.

Lambert is frequently getting caught in political crossfire between supervisors. Although he serves at the pleasure of the board and is supposed to carry out the wishes of its majority, deciding who belongs to the majority and what it wants is becoming an increasingly dangerous and stressful exercise for Lambert, according to his associates.

When a speaker called for his firing during a budget hearing this year, the crowd burst into applause. A recent editorial in the Washington Times criticized a 3 percent salary increase for Lambert, noted that he does not have a college degree and said "it seems that Mr. Lambert's raise is based on the political protection he provides for the Board of Supervisors, not for the service he performs for the taxpayers."

Robert C. Kelly of Hazel/Peterson Cos., a prominent development firm, said in Lambert's defense: "I think that J has unfairly become the target for everything that's wrong in the county. Whatever J's shortcomings were four years ago when everybody loved him, they're the same set of shortcomings now."

Lambert is so closely associated with Fairfax and the county Board of Supervisors that, as its stock goes, so goes his. As the county's reputation soared in the 1980s, so did Lambert's.

Now, board Chairman Audrey Moore (D) is under fire from the business community for pushing business tax increases and curbs on development, and from other board members for what they say is a lack of leadership. The county's economy is in a slump, residents are complaining about tax increases and the board is having difficulty speaking with one voice on anything. In these circumstances, Lambert has become a lightning rod for complaints.

Republican Party officials, who asked not to be identified, said they think Lambert could be presented as a political liability for the board's seven Democrats in the November 1991 elections. The Republicans cited some public resentment over Lambert's $129,348 annual salary and the growing size and cost of county government.

Supervisor Thomas M. Davis III (R-Mason), a likely challenger to Moore for the chairman's seat, told the Fairfax Newsletter that he was "completely disillusioned with the county's political and bureaucratic leadership." The Newsletter quoted Davis as saying, "The only way to change it is to change some people."

Davis said yesterday: "I think J feels he's been following the edicts of the board majority, but I've been very frustrated by some of the decisions coming out of his office. Consequently, when his pay raise came up, I voted no. But he's a very capable guy who brings a lot of institutional knowledge and history to his decisions . . . . I'm not out there calling for his resignation."

For his part, Lambert said: "If I thought my services were no longer desired by the governing body, I'd have no difficulty in leaving the government. As far as the criticisms, I think some of them are warranted, some of them are not. I've never professed to be anything but what I am, and that certainly is not perfect."