Controversial former Fairfax County sheriff James D. Swinson has been hired as a part-time deputy by his hand-picked successor to give advice on the departments budget and other key management matters.

"When the sheriff leaves, I don't become all-knowing about what's happened in the past," said Sheriff M. Wayne Huggins, who worked for nearly two years as Swinson's chief deputy before taking office earlier this month. "I've had to call him several times."

Swinston, a Republican, who made $48,900 as sheriff, earns $3.55 and hour as a part-time deputy. According to Huggins, Swinson has worked between 12 and 16 hours since Jan. 1. The appointment is effective for a year, but Huggins said Swinson "probably will not be used after six months."

Swinson was out of town yesterday and could not be reached for comment.

Word of his new part-time position drew immediate fire yesterday from Fairfax Democrats.

Supervisor James M. Scott (D-Providence) called Huggins' decision to hire Swinson a "very unwise move."

"It would be much better for everybody concerned," Scott said, "if the new administration completely separated itself from the old one."

Emilie Miller, the outgoing county Democratic chairman, said the appointment demonstrates that Swinson, not Huggins, is still running the department.

She said Huggins "needs Swinson's advice because Huggins doesn't know how to be sheriff."

Referring to Swinson's controversial running of the county jail, she said she doubted there would be improvements under Huggins because "we're going to keep seeing Swinson, and his relatives and his handpicked people" directing the department.

Huggins was accused of cronyism last month when he selected Swinson's son-in-law, Carl Ray Peed, to be chief deputy at a salary of $30,000-a-year.

At the time of his appointment, Peed held the rank of captain, a position he reached after working in the department five years.

In defending his selection of Peed, Huggins rejected suggestions of favoritism, saying that Peed "best fulfilled my criteria."

Swinson, who established himself as the best local Republican vote-getter in Virginia's largest and richest county, came under fire in recent years from critics who accused him of general mismanagement of the new county jail.

Investigations disclosed widespread misuse of jail inmates by deputies who put prisoners to work outside the jail as unpaid laborers.

But he received the most criticism when three people died after being confined in the jail.

Late last year, Swinson and Huggins reached an out-of-court settlement, reportedly for $10,000, with the estate of a woman who died in the jail.

A lawsuit involving the death of Donald Ferguson, another prisoner who died after confinement in the jail in late 1978, is pending.

Huggins said one of the tasks Swinson is being compensated for is the time he spends with lawyers preparing the department's defense in the Ferguson case.

The 14 other part-time deputies fill in as bailiffs, deputies who escort prisoners to and from court, but Huggins said Swinson will not perform bailiff's duties.

Huggins, noting that the proposed 1981 budget under review was put together under Swinson, said county officials "may ask me questions I can't answer. I was not there and not privy to what's gone on in the past. With him [Swinson] right there, I can defer to him."

Swinson collects a sheriff's retirement salary of $14,000 a year from the county, as well as retirement benefits for military service. He gets no fringe benefits as a part-time deputy.

Huggins said he considers Swinson's part-time salary low for the work he does, and is paid only for the hours he works.

"It's a shame we can pay him only that little," Huggins said. "But at least it will help pay for his gas."