A Fairfax-based developer wants the Town of Leesburg to change its height restrictions to allow high-rise office buildings in areas zoned for mixed use, a move that worries some town planners and leaders who say it could cause unwanted development and ruin the town's aesthetic character.

Peterson Cos., formerly HP Cos., has asked the town for a special exception to raise the height limit for buildings in mixed-use areas from 45 feet to 100 feet. The company wants permission to build a six-story, 75-foot office building on 150 acres south of Route 7 at Cochran Mill Road (Route 653) across from Harper Park Middle School.

The proposed Leesburg Commons project also calls for 580,000 square feet of retail space, including a day-care center, a hotel, restaurants and shops, company Vice President Robert W. "Chip" Burton said.

A subcommittee of the town's Planning Commission is expected to review the plans tonight and make its recommendation in a few weeks. But the Town Council delivered a blow to the project Tuesday night after denying a request from the developer to amend the town plan to allow for a diamond interchange instead of a cloverleaf at the proposed Route 7 entrance to the shopping center. The developer has said the diamond interchange would take less space, but planning commissioners and town planners want to follow the town's plan and are concerned about the increased traffic the project would generate, as well as the building's proposed height.

"The applicant is being cooperative, but we can't commit right now," said Gus Glikas, chairman of the Planning Commission and a member of the subcommittee. "We have to know what effect that tall of a building will have on the town. We need to look at how it is from the road. We don't want Route 7 to look like any other area that is congested with office buildings."

Some town planners and area developers suggested that the proposed office building be set back from Route 7 and surrounded by shorter office buildings so it would not stand out as much. Still, it would be one of the tallest buildings in the town limits. Now the tallest building within the town's limits is the five-floor Loudoun County Government Center at about 90 feet at Harrison and Loudoun streets, according to town planners.

"This is an example of the kind of things we need, but it's not in the right location," said Cemile Bingol, the Loudoun County representative to the Piedmont Environmental Council. "Do we really need another 600,000-square-foot retail space in Leesburg? We have too much of that already. This would be sprawling out to the edges of Leesburg."

Burton said the retail uses probably would be built first, with the office development phased in as the need arises. Burton and local economic development officials said many companies are looking for office space in the town's 11-square-mile limits but can't find enough space fast enough.

"We have no plans to build a 100-foot office building at Leesburg Commons," Burton said. "But we thought having the ability to do that would help Leesburg be more competitive" in the office market.

Town Council member Kristen C. Umstattd, the council's representative to the Planning Commission, said she understands the need for more office space in Leesburg, but she expressed concern about the development mix at the Leesburg Commons property.

"One way to recoup our office potential is to allow taller office buildings," she said. "On the other hand, there are concerns from citizens that they don't want the gateway to Leesburg to look like Tysons Corner. We're going to have a battle between keeping the entrance to Leesburg . . . as low-key and in compliance with the historic traditions and trying to build up a large office space."

Peterson Cos., headed by developer Milton V. Peterson, is one of the Washington area's major development companies. It has developed commercial, retail and residential projects including Fair Lakes Promenade, the Tyson/McLean Office Park and the Washingtonian Center in Gaithersburg. The company now is seeking to build National Harbor, a $1 billion resort on the Potomac shore in Prince George's County.

Burton said the company plans to begin construction on the Leesburg Commons project next summer or fall.