A multimillion-dollar expansion of Potomac Mills mall in Prince William County set to start this fall has yet to receive approval from the county's planning and zoning board.

The plans by Indianapolis-based Simon Property Group, which owns the mall, include adding a Neiman Marcus Last Call Clearance Center to the roster of more than 200 stores. Plans are to build a 50,000-square-foot addition.

The Prince William County Planning Office has seen no filings for building permits.

"The first we heard about it was when we saw it on the news," said a woman answering the phone at the planning office yesterday.

The process to obtain permission for a project this large usually takes months, but Corey A. Stewart, chairman of the Prince William Board of County Supervisors, said yesterday that he sees no problems getting the necessary approvals.

"We're going to get it through for them. If I have to, I'll get personally involved," he said.

He defined personal involvement as "keeping an eye on county staff" to make sure there are no delays.

The process involves approval at several levels of county government and public meetings.

A delay, however slight, could push back construction, which the company said would be completed next spring.

A potential setback to development is resident opposition, but Simon Property has a fan in one community conservation group.

Kim Hosen, executive director of the Prince William Conservation Alliance, a community organization, said the group supports expansion and would not block the company's attempt to get approvals.

She cited assurances from mall management that the renovation would make the center more energy efficient and that it was increasing square footage on property it owns.

Les Morris, spokesman for Simon Property, said it's common for the company to make announcements before starting the approval process.

Morris would not disclose how much the addition to the mall would cost, but said it was several million dollars.

Neiman Marcus Last Call Clearance Center will move into an existing 34,000-square-foot space between the Off Broadway Shoe Warehouse and AMC Theatres.

The expansion will feature 20,000 square feet of retail space, 30,000 square feet for restaurants and a redesigned main entrance and exterior facade that one member of mall management said would bring a more parklike atmosphere to the south side of the property.

Potomac Mills Mall is a top tourist destination in the state, according to survey by the Virginia Tourism Corp. Contact Louis Llovio at (804) 649-6348 or LLLovio@timesdispatch.com.