Fairfax County Sheriff-elect M. Wayne Huggins yesterday named the son-in-law of his political mentor, retiring sheriff James D. Swinson, to be his chief deputy at a salary of $30,000 a year.

Huggins rejected suggestions that cronyism was a factor in his selection of Carl Ray Peed, a sheriff's department employe for the past five years, to succeed him as chief deputy.

The sheriff-elect, who will take control of the jail and department from Swinson next month, told a news conference that he selected Peed because he "best fulfilled my criteria for youth, an excellent background in corrections, (and is) someone who is both ambitious and agressive."

The appointment drew prompt criticism from County Supervisor Alan H. Magazine, who said the selection of Peed "has a bad odor to it . . . It looks like the 'good old boy' network is still in effect."

During his recent campaign for the sheriff's position, Huggins, 30, a former state police office, had tended to avoid mentioning Swinson, whom he once called "the best sheriff in Virginia."

At his news conference yesterday, Huggins came close to acknowledging that there had been serious problems during Swinson's administration, and pledged that he would "run a jail that is open to public scrutiny." He said he would inaugurate a drug counseling program for inmates and create an internal investigative unit on his staff in an effort to "professionalize" jail operations.

Later yesterday, Fairfax prosecutor Robert F. Horan Jr. disagreed with the decision to create an internal investigation unit.

Sheriffs' deputies, he said, "have no training . . . they are jailers and bailiffs," while police "are fully trained and qualified for investigative work." Horan, a Democrat, said "a good independent investigation by the police department, one of the finest around, is the way to handle a crime within the jail."

Supervisor Magazine questioned Swinson sharply about Peed's rapid rise in the sheriff's department during an August 1978 hearing into the jail's operation.

At that time Peed held the rank of captain and was said to have risen rapidly from the position of corporal, which he held when Swinson hired him in 1974. "I don't have any problems with that (Peed's promotions) at all," Swinson told the County Board during the 1978 hearing.

Huggins, a Republican who defeated three other candidates in the Nov. 6 elections, said yesterday he selected Peed over three other candidates. The others lacked "corrections experience," the sheriff-elect said. Peed taught at the Virginia State Department of Corrections Training Academy in Waynesboro before he joined Swinson's staff.

Huggins said he believed procedural changes -- not a purging of the jail's staff -- could help improve the county jails image. The jail has been the focus of much criticism and two investigations following the deaths of three people who were held there.

The two investigations produced sharply different findings. One authorized by Republican Gov. John N. Dalton concluded that Donald P. Ferguson, an inmate who died after confinement at the jail in late 1978, had not been mistreated there.

That report contradicted one issued earlier by a panel of Northern Virginia Democrats who said Ferguson would not have died if he had been properly treated. The Dalton report criticized the jail's failure to forward medical records about the man's condition when he was transferred from the jail to Western State Hospital in Staunton, where he died two days later.

"Nobody prayed more than I did before my election," Huggins said. "And I promised that there would be no mass firings, no vengeance. We're starting with a clean slate here."

Huggins said the effort to improve medical treatment for the 11,000 people who pass through the jail each year will focus on findings of a recent study that indicated that 94 percent of the 252 inmates in custody in early November "were under the influence of alcohol or other drugs when arrested."

Huggins said he plans to invite area colleges to send graduate and medical students to help with substance abuse counseling at the jail.

The internal affairs until will be used to "handle complaints by citizens and inmates, investigate lawsuits against the jail, and to investigate crimes committed inside the jail," Huggins said.

"There has never been a person to coordinate this before," Huggins said. He added that the unit will be run by "a person with a wealth of criminal investigations experience." CAPTION: Picture, M. WAYNE HUGGINS . . . "starting with a clean slate"