The owners of the Tysons Corner Center are planning a $50 million renovation and expansion that would add an underground level and two new department stores to the mall, increasing its size by roughly 30 percent.

Geoffrey M. Donoghue, vice president and director of development for Lehndorff Tysons Joint Venture, said the expansion would make room for at least 60 new specialty shops. He also said his firm expects to build four multistory parking garages containing a total of 7,000 spaces near the existing major department stores.

The center's owners said they want to start construction on the first anchor store and one parking garage by early fall.

However, county officials, who already face severe transportation problems in the surrounding area, expressed concern about the additional traffic that would be generated by the expansion.

The 90-acre shopping center is in the middle of Fairfax County's fastest-growing commercial region. A second shopping center, known as Tysons II, along with 10 office buildings and two hotels, is planned on 107 acres directly across Rte. 123. That road itself is a major artery through Tysons Corner, where 13 million square feet of office space have been built in recent years.

Other developers have promised more than $17 million in road improvements in the Tysons Corner area, and county officials fear that those would be overwhelmed as soon as they are completed.

"Any additional development at Tysons has got to raise the question about whether the road network can handle the traffic," said Supervisor James Scott, whose Providence District includes the mall.

The additional anchor stores would occupy new buildings adjoining the current mall, Donoghue said. Space for the other new stores would be created by enlarging a tunnel that runs under most of the existing shopping mall. That space has been used primarily for storage, he said.

Plans call for cutting through the existing mall floor to create a central two-story atrium opening to the new lower level. The existing mall would become the second level of the new center, according to plans.

"As part of major interior renovations we will install skylights" in the roof of the mall, Donoghue said.

The mall now contains 1.3 million square feet of space, Lehndorff officials said. They were reluctant to give the expansion's exact square footage because the size of the new anchor stores is not yet known, but they expect the project to add at least 400,000 square feet.

Lehndorff bought the shopping center in February 1985. Earlier this week, Nordstrom Inc., a Seattle-based fashion retailer, announced plans to open an anchor store in the shopping center. Donoghue said negotiations are under way for the second new anchor but "there is no deal yet." Major stores at Tysons are Woodward & Lothrop, Hecht's and Bloomingdale's.

Shiva Pant, head of the county's Office of Transportation Planning, said the center's owners are likely to have to make major road improvements and further upgrade the parking if they expect the county's Department of Environmental Management to approve site plans required for the expansion.

He said the current parking capacity of 6,400 cars fails to meet the county code for the mall.

Lehndorff officials said that in addition to the 7,000 spaces in the new parking garages, there would be 1,500 additional surface parking spots on the other side of nearby International Drive. That would give the expanded center a total of 8,500 parking spaces, but even that is far short of the more than 10,000 spaces local civic leaders and other developers predict would be needed when the expansion is completed.

"We are simply looking at the proposal from the overall impact on the area. The original owners did absolutely nothing to help alleviate traffic problems. If they plan to add 60 more stores and two anchors, we have to make sure the public interest is protected," Pant said.

Fairfax Board Chairman John F. Herrity said "everything will have to be brought up to code" before expansion can take place."

Homart Development Co. and the Lerner Cos., joint venture partners in the Tysons II office and shopping center project across Rte. 123, had to argee to spend more than $14 million in road improvements before getting Fairfax to approve that project.

Supervisor Nancy Falck vowed to make sure plans by Lehndorff did not overpower road improvements under way on Rte. 123 or at Rte. 123 and International Drive.

Ed Prichard, project attorney, said plans "to bring International Drive up to state standards to hook up with Gallows Road" were submitted several weeks ago to county and state officials.

However, Linda South, a spokeswoman for the Virginia Department of Highways and Transportation, said plans had been sent back to developers because highway officials did not have sufficient information to make a decision.