The director of the District's Department of Corrections has forbidden his staff to assign known sex offenders to female prison employes to test their reactions after an employe at the Lorton prison complex complained about the practice.

In a memorandum dated March 2, Director James F. Palmer wrote "the deliberate assignment of dangerous male sex offenders to female employes, in order to evaluate an inmate's rehabilitative progress, is a prohibited activity."

The memo, to be posted on all department bulletin boards until April 30, also says that "the deliberate assignment of female employes, as experimental objects in male rehabilitative programs, is a prohibited activity."

The memo stemmed from a complaint filed in 1979 with the U.S. Equal Employment Opportunity Commission by Kay Duffy, a teacher at the youth center at Lorton. Duffy complained that sex offenders were assigned to female staffers to find out if the inmates were ready to deal with women and the outside world.

Duffy charged that the policy was discriminatory because it afforded less security to female employes than to male employes, according to Ken Bynum, president of Local 1550 of the American Federation of Government Employees. The union represented Duffy at hearings in the case.

Bynum said the complaint stemmed from the assignment to the prison school building of a sex offender who had previously raped a prison psychologist and tried to rape a teacher at Lorton.

Duffy was given lower ratings and denied a promotion, according to the union. Last December, the EEOC ruled that Duffy, who is still an instructor at Lorton, must be given a promotion and back pay and that the corrections department must pay all her legal fees.

Donald Soskin, the department's judicial affairs officer, said the assignment of sex offenders to female employes was not a broad department policy, but was an isolated case. "I know of no similar complaints," he said.

Soskin added that Duffy "was never attacked. She did not suffer any physical harm."

In addition to the other instructions, the memo said: "All instances of inmate misconduct, when reported by female staff members, will be treated as seriously as those reported by male staff members."

Meanwhile, the Fairfax County Board of Supervisors yesterday continued its long-running attack on Lorton, which houses District prisoners but is located in southern Fairfax.

The board asked the county attorney to determine if land use, zoning or planning laws may provide a legal mechanism for controlling expansion planned at Lorton.

The move was initiated by Chairman John F. Herrity, a Republican, who toured Lorton Saturday, a day after Supervisor Sandra Duckworth, Democrat of Mount Vernon, toured the facility with D.C. Mayor Marion Barry.

Herrity suggested that Duckworth, who Friday praised city officials for recent efforts to beef up security, may have been naive for letting Barry conduct the tour. Herrity said District officials "deliberately tried to conceal" things on that tour. Duckworth responded that although Barry did have a set agenda, "they went where I wanted to go."