Northern Virginia's most prominent land developer and the nation's largest shopping mall builder said yesterday they are teaming up to build a 1.2 million-square-foot mall adjacent to the Manassas National Battlefield Park in Prince William County.

William Center Mall, which will be part of a project that also will include residential and office space, will be one of the largest shopping centers in the Washington area when it opens in 1992. Retail experts say the mall will significantly increase the already intense competition among Northern Virginia malls, particularly affecting Fair Oaks Shopping Center, which is just eight miles east on I-66 in Fairfax County.

The project, whose price tag has not been released, also will be a milestone in Prince William's efforts to become a major player in the local commercial real estate market.

"It excites me in the sense that we're no longer going to stand in the shadow of Fairfax County," said Prince William Supervisor Robert L. Cole (D), whose Gainesville district includes William Center. "This is going to be nicer than Fair Oaks."

The real estate developer, Hazel-Peterson Cos., and the shopping center builder, Edward J. DeBartolo Corp., included the plans for the mall in a site plan submitted yesterday to develop William Center, a 600-acre commercial, retail and residential development along I-66 and Rte. 29. When completely finished in 1999, the project will have 560 new homes and 1.7 million square feet of office space in addition to the shopping center.

Company officials said they expect to begin constructing an office building and the homes this spring and to begin work on the shopping mall within the next two years. The site now is a combination of woods and fields.

It is not known yet which retailers will locate in the new shopping mall. Richard S. Sokolov, senior vice president of development for DeBartolo Corp., said the mall will have five major department stores, and the company is talking to local and national retailers about locating in the shopping center.

The planned mall is the second in the Washington area for DeBartolo, which owns and operates dozens of major shopping centers around the nation. DeBartolo is currently developing a mall at the Bowie New Town Center project in Maryland.

Within a 25-mile radius of the future site of the William Center Mall, there are already three existing shopping centers, a fourth under construction and a fifth in the planning stage. Local retailing officials say William Center's main competitor is likely to be the 1.4-million-square-foot Fair Oaks mall at the intersection of Rte. 50 and I-66, which has 213 stores, including Hecht's, Woodward & Lothrop, Garfinckel's, Lord & Taylor, Sears, and J.C. Penney outlets.

DeBartolo and Hazel-Peterson officials said they expect their new mall to serve as "an enviable interceptor" to traffic that otherwise would be headed to Fair Oaks and other nearby shopping centers.

Gil Brooker, general manager of Fair Oaks, said he believed the area will be able to support both malls. The more the competition, the greater the choice consumers will have, he said.

"I think it all depends on the quality of stores in the center," Brooker said. "We know that we have quality here and that we have a broad selection of stores that serves all segments of the consumer market."

Sokolov said, "We feel we're far enough away from Fair Oaks for our project to work."

Tysons Corner Shopping Center and the new Tyson II mall, as well as the planned Dulles Town Center (formerly Windmill) regional shopping center being developed by Lerner Cos. at Rtes. 7 and 28 in Loudoun County also are expected to provide competition for the new mall. In addition, Potomac Mills, a 1.3 million-square-foot discount retail shopping center, is located in Prince William County off I-95 in Woodbridge -- about 20 miles south of William Center.

The planned mall will tap into one of the Washington area's fastest-growing counties. Prince William had an average family income of $44,889 and a population of more than 200,000 last year. The county's population is projected to reach 240,000 by 1990 and more than 300,000 by the year 2000, according to county officials.

The rapid growth, however, isn't sitting well with many local residents and Civil War history buffs, who have opposed William Center since Hazel/Peterson officials first suggested the project as an office and residential complex two years ago. Many residents said they fear that William Center will destroy an area known for its rich farmlands and grassy battlefields.

"It would destroy western Prince William and it would destroy the battlefield," said Annie D. Snyder, a leading civic activist who lives near William Center. "How long do you think this rural area could survive the influx of all those people who would come with a mall? ... We'll fight it with everything we've got."

Neighbors of the planned project also complained yesterday that they were not aware that Hazel/Peterson had planned a shopping mall for the site.

"I feel we've been deceived," said Philomena Hefter, a western Prince William resident.

John T. (Til) Hazel, an owner of Hazel/Peterson, said yesterday that his firm had been trying to attract a major corporate headquarters to the property, but recently decided that a mall was needed as a "catalytic agent" to attract corporate offices on the remaining acreage at William Center.

"That's been the history of malls all over the country -- that they bring along offices," Hazel said.

Disgruntled county residents may have no opportunity to challenge the shopping center, however. The William Center property was rezoned by the Board of County Supervisors in 1986, shortly after Hazel/Peterson purchased the land, and county officials said yesterday that the site plan filed by Hazel-Peterson yesterday must be approved only by the county's Department of Development Administration. No public hearings or additional action by the supervisors are expected, the officials said.