Loudoun County officials are balking at a proposal by George Washington University and two developers to build a massive educational, residential and office complex, because they fear it would worsen traffic congestion on the heavily used thoroughfare Route 7.

After a six-hour public hearing recently, the county's planning commission voted to let the Board of Supervisors decide whether it wants to approve the 576-acre University Center complex. The mixed-use development, a joint venture of GWU, the Smith Cos. and the Michael Swerdlow Cos., would be in an area where several major developments have been proposed.

Numerous county officials said they support the university's planned presence in Loudoun. But they said they are concerned that they might create a traffic nightmare if they allow the university to build educational facilities alongside office and retail space, single-family houses and a research and development park. County officials already have opposed parts of the developers' plans.

"No one is anti-GWU or anti-Charles E. Smith, but the Board of Supervisors has the final authority on this and we have to face our constituents," said Betty W. Tatum, the board's chairwoman. "If you have people tell you it now takes them two or three times longer to get to work than it did two years ago, then you have to take a serious look at the impact on transportation."

Steven W. Stockman, a county supervisor representing a district near the proposed University Center development, said the project is a "tremendous opportunity for the county. "This project has been given a bad rap because people who opposed it call it the 'Crystal City of Loudoun,' " he said. "To call it a Crystal City is hogwash. It's a keystone of development in the county. We need to sit down with the developer and work out the details."

Greg Pohle, vice president of development for the Smith Cos., said the firm has worked hard to respond to the planning commission's concerns about traffic, building design and the density of the project.

"We've lowered the density and building heights along Route 7, revised the master plan to build on the side of the ridge and preserve the trees, and removed all buildings from the flood plain," he said. "We know transportation is a critical issue and it is an important issue to the future economic development of the county."

Pohle said construction of university facilities alone at that site would not be possible without the commercial development. He said 20 percent of the developers' profits would go to the university.

"This is an appropriate location for the project," he said. "It's at the intersection of two major arteries {routes 7 and 28} and lends itself to the county's goal of bringing high quality high-technology and research and development companies to the county."

Under the original plan, GWU and the Smith Cos., the main development partners, said they wanted to have the land, presently zoned for agricultural use, rezoned to a category called planned development/research and development park. They initially proposed a project that would have 14.7 million square feet of office space, 433 apartments and a graduate engineering school.

The site is adjacent to a collection of other huge projects, including Lansdowne, which is expected to have more than 12 million square feet of office space, 2,000 luxury houses and 120,000 square feet of retail space.

Last June, under pressure from county officials, GWU and Smith revised their plans, reducing the amount of office space and lowering building heights. Two weeks ago, the developers submitted yet another proposal with a more detailed traffic study, but that did not satisfy county officials.

Under the revised plan, GWU and Smith are asking the county to approve the project with a maximum of 2.1 million square feet of space for GWU and 9.5 million square feet for the office and research and development park. They also said they would agree to other development restrictions.

The new proposal also calls for construction of six buildings that would be no taller than 150 feet, down from the original plan calling for 195-feet buildings along Route 7. The plan also calls for $43 million in road improvements, including widening Route 7 in front of the project, extending Route 607 through the development, and building two bridges over Route 7.

GWU, Smith and county officials are scheduled to meet with Virginia Highway Department representatives within the next two weeks to resolve additional concerns about traffic and building design.

If the project is approved by the end of the year, the developers said they will still be able to open the campus by September 1989. If the campus is eventually built, an estimated 450 students are expected to attend class there. GWU hopes to assist high-technology, communications and research and development companies moving to the area.

"Right now, that location is a very bucolic scene: There's open space, trees and cows," said Chairwoman Tatum. "We're looking at the GWU and Smith project as part of the entire picture of Loudoun County. What we do at one end of the county will impact the other end."

Loudoun Supervisor Charles Bos said the concerns about density and design only highlight the need for the board to meet to discuss development in the county.

"It's not a simple issue," he said. "This project is a logical extention of what we've had in the past, but we're at a critical point where we can no longer talk about these development issues in bits and pieces."