For nearly 16 years in Fairfax County Republican politics, the rule has been that only a fool or a Democrat runs against Sheriff James D. Swinson, the garrulous country boy who for four years has been the GOP's leading vote-center.

And yesterday, after more than a year of highly publicized criticism about how the sheriff runs the county jail, Swinson's sway over Fairfax Republicans held fast.

The retiring sheriff's chosen successor, M. Wayne Huggins, soundly defeated Myron L. (Bud) Greenquist, whom Swinson fired from the sheriff's department last year. Greenquist, careful not to belittle Swinson directly, tried and failed to change Republican voting habits by critizing "the disturbing events" at the jail.

The Republican's enduring affection for Swinson and the candidate whom Swinson supports delights Kenneth R. Wilson, the winner of yesterday's Democratic primary for sheriff. Wilson, the recently retired deputy chief of the Fairfax Police Department has said that he plans to campaign against certain "irregularities" at the jail.

Those irregularities include the deaths of three inmates who died after confinement in the $4.6 million jail, a finding of negligence on the part of jail personnel in one of the deaths, an investigation of alleged misuse of inmates by sheriff's deputies and the admitted perjury of the chief jailer who used inmates to pour concrete at Swinson's home.

Wilson claims to have new information on misconduction at the jail that was information that he did not choose to reveal to win nearly 60 percent of yesterday's vote and defeat Terry C. Armstrong, a former senior corrections officer for the District of Columbia.

"I don't want to shoot it all on this primary," Wilson had said.

Wilson, 46, promises that if he is elected in November he will take a close look at the deputies running the county jail and get rid of those responsible for past mistakes.

Huggins, 30, a former Virginia state trooper who has been chief deputy in the sheriff's department for the past year, may face the difficult task in the upcoming campaign of both defending his handling of the jail problems and separating himself from bad publicity about Swinson.

Huggins' task was made more difficult last week when he was sued in U.S. District Court by the family of a woman who died last July after staying in the jail. The suit claims that Phyllis Sanders died because of "callous and indifferent" action by Huggins and others at the jail. Huggins specifically accused in the suit of conspiring to "withhold and destroyed evidence" related to Sanders' death.

Huggins says the allegations against him are "ridiculous." He has devoted his campaign to discussing the future of the sheriffs department and the possible building of a treatment center for alcoholics.

For his part, Swinson, 66,, has said little in the campaign. In fact, the sheriff has refused to speak publicly for several months, largely because off attacks from critics who've called him callous and incompetent.

The former Marine lieutenant with the booming voice and down-home charm has been depressed by a year of what he has called "witch hunts," according to personal friends.

Last fall, Swinson told a reporter "it is unfortunate that near the end of my career I have to go through so much of this horse - - -."