The federal General Accounting Office has asked the D.C. government why it continues to lease property near Lorton Reformatory to the Vulcan Materials Co. in light of a long-festering complaint that the firm allegedly discriminated against four black truck drivers.

Vulcan leases 55 acres in Fairfax County from the District to operate the Occoquan stone quarry, which produces crushed stone for construction projects. The company is negotiating with the D.C. Department of General Services for 90 more acres.

Last January, the D.C. Office of Human Rights issued a "probable cause" finding that Vulcan and a trucking subcontractor, A.G. Van Metre Jr. Inc., had systematically assigned less profitable stone-hauling routes to four independent black drivers between late 1978 and December 1981.

The human rights office report, prepared at the request of DGS, also said there was evidence that supervisors at the quarry had called drivers "niggers" and had discriminated in their layoff and recall policies. Lawyers for Vulcan have denied all the allegations and contend the human rights office conducted a "shoddy," one-sided investigation.

The attorneys also said that the drivers, Milton F. Wright, Levi Harris, Antonio A. Correia and Charles E. Miles Jr., have lodged the same complaint with a variety of federal and state agencies in an effort to force a cash settlement, but to no avail.

"The allegations are just wild," said Wesley S. Williams Jr., a lawyer representing Vulcan.

The GAO entered the case Oct. 7 at the request of Rep. Parren Mitchell (D-Md.), whose office had been contacted by the drivers. In a letter to John Touchstone, director of DGS, the GAO asked for a justification for the city's plans to expand its current $22,100-a-year lease agreement with Vulcan.

"I would like to know what actions, if any, are being considered to prevent a recurrence of the problems alleged . . . ," Henry R. Wray, GAO's assistant general counsel, said in the letter. "Also, in light of the findings of the human rights office investigation, has the District considered whether it is appropriate to engage in new and further dealings with Vulcan?"

The current agreement authorizes the city to cancel the lease if Vulcan or a subcontractor is found to have discriminated against its employes on the basis of race or sex.

But Touchstone said last week that he has been advised by the D.C. Corporation Counsel's office that the anti-discrimination clause is not applicable to independent haulers, like the four black drivers, who worked for but were not employes of the Van Metre trucking firm.

Touchstone said DGS has proposed language for a new lease agreement with Vulcan that for the first time would extend the protection of the anti-discrimination clause to all persons employed at the site, including independent haulers.

One of the drivers, who declined to be identified, said last week that Touchstone and other DGS officials appear to be "bending over backwards" to accommodate Vulcan.