To revenue-hungry Prince William County planners and politicians, the project must have sounded mouthwatering.

A big-shot developer with a reputation for building swank projects on a giant scale was proposing to build the largest discount mall in the country just off Interstate 95, a 1.2-million-square-foot emporium that would feature 120 separate outlets, many of them selling upscale designer products.

Across from the mall would be more shopping complexes and office buildings.

The numbers attached to the project also were staggering. The developer, Western Development Corp., had sunk nearly $200 million into the project. Western had estimated that by the time the project is completed toward the end of the decade, it would generate more than 6,500 jobs, $10.2 million in state tax revenues annually, and $4.5 million in annual net fiscal benefit to the county.

Prince William County could hardly afford to say no, and it didn't. Part of the mall is under construction and scheduled to open next spring, and the County Board of Supervisors approved the final 55-acre segment of the massive project Tuesday night.

But in giving that approval, the supervisors, by their staff's own reckoning, set the clock ticking on a traffic time bomb that will have to be defused in the coming years.

"The traffic issue is not easily resolved," county Planning Director Roger Snyder told the board before it voted, 6 to 0, to approve the final rezoning sought by Western.

Prince William County, which is heavily populated by commuters, has recently stepped up efforts to attract more business and commercial development, which it considers a subsidy for further residential development. Along with a large IBM plant in western Prince William, the outlet mall is the most significant development in the fast-growing county.

Although Western agreed to put more than $5 million toward road improvements in and around the project, located just west of I-95, between Telegraph and Smoketown roads, county planners warned of long waits at intersections in the area and backed-up traffic in all roads leading from the project.

C. Lacey Compton Jr., attorney for Western, acknowledged that the project would create severe traffic problems for the county. But he added: "The jobs and revenue created by this development would more than offset any problems it may create."

Compton further suggested that the county could apply some of the new revenue to building roads to ease increased traffic in the vicinity of the Washington Outlet Mall.

Western officials say the outlet mall will be an upscale project. "The quality level will go even beyond Tysons Corner," said Western President Herbert S. Miller, referring to the huge development adjacent to the Beltway in Fairfax County. "It will be a showpiece for Prince William County, and like Tysons, it will have a major impact on the whole metropolitan area."

Miller said he expects the mall to draw shoppers looking for discount prices from Baltimore to Richmond, and to compete with a large group of factory outlet stores in Reading, Pa.

Western Development Corp. is well known in the metropolitan area for developing Georgetown Park, a fashionable shopping mall, Washington Harbour, a development on the Georgetown waterfront and Market Square, a residential and office complex on Pennsylvania Avenue NW.