Fairfax County Sheriff James B. Swinson, whose department is under investigation by the Fairfax prosecutor has hired as his chief deputy a former Virginia state trooper who is being introduced around the county as Swinson's possible successor.

M. Wayne Huggins, a 29-year-old former president of the Virginia State Police Association, was hired 19 days ago to replace former Chief Deputy Sheriff Myron L. Greenquist, who was fired from his $26,400-a-year job in early February.

Greenquist was fired, according to Swinson, because "we could not work as a team." Greenquist said yesterday he was fired "to put the fear of God into the rest of the deputies" in regards to Commonwealth's Attorney Robert F. Horan's investigation of the sheriff's department.

Swinson said yesterday he has not yet decided whether he will seek a fifth term as sheriff next year. He said he was aware of Huggins' interest in the sheriff's job and added, "I certainly am going to make every effort to see that Mr. Huggins is getting every opportunity he can to learn about the job."

Some political observers in Fairfax County and in Richmond said Huggins is being groomed as the Republican candidate for sheriff in next year's election. At the county Republican convention in April, Huggins was introduced to party members as "the next Republican candidate for sheriff" by James R. Tate, a member of the Fairfax County Republican Committee and a former Virginia delegate.

"Let me ask you this," Tate said yesterday, "if you are sheriff, would you bring in a guy like Wayne Huggins and run against him?"

Huggins, a state trooper for seven years, founded and was first president at state police organization that urged the adoption of the so-called police officers' bill of rights by the legislature. Virginia Secretary of Public Safety Selwyn Smith, a Democrat, yesterday called Huggins "a tremendously capable young man with exceptional leadership ability."

Huggins described himself as and aggressive" and said, "I'm going to know all there is to know (about the sheriff's job by this time next year."

The job Huggins is seeking has been surrounded for months by allegations of improbriety concerning use of county jail inmates to do work for Swinson and other sheriff's department employes.

Prosecutor Horan has said he is looking into allegations that an innate built an expensive stone fireplace in the sheriff's house.

Horan also is investigating allegations that some inmates were allowed to visit their wives or girl friends when they should have been in jail, and checking the circumstances under which Swinson received chain-link fencing that divides his $100,000 Great Falls home from an adjacent wooded area.

Horan repeatedly has told The Washington Post over the past three months that he will soon announce the findings of his investigation. Horan could not be reached yesterday for comment on the investigation, although sources in Richmond confirm that Horan has been checking with the Virginia Department of Corrections on the proper procedure for operating county jails.

Swinson said yesterday that Horan's delay in the investigation indicates that the jail has been operating as it should. "Did you ever stop and think," Swinson said, "that maybe there wasn't anything to come up with?"