When residents of North Farm in Rockville complained about the height of a proposed office building near their subdivision, the developer, Westmont Associates, attempted to ease their concerns.

It sent a tethered weather balloon aloft until it reached the height of the 15-story building, so residents could see for themselves whether the tower would infringe on their neighborhood.

"They were right," said John T. Kenney, a Westmont executive. "The 15-story building was too high. We've already told them we'll reduce it by about 60 feet off the top."

The weather balloon was a smooth public relations move, but easing other citizen concerns about the development might not be quite as easy for the McLean firm, which specializes in developing office parks in the Washington area.

The property abuts nearby subdivisions such as North Farm, where homes sell for $120,000 and up, and the proposed development, predictably, has encountered well-organized citizen opposition.

While the office tower has been a major sore point, residents also have complained about traffic congestion and the incompatibility of the project with residential areas east of the site.

"These roads are virtually impassable now during rush hour, and they're projecting 10,000 cars a day through our neighborhood," said Mark Allen, president of the North Farm Citizens Association.

The company has proposed building 2.5 million square feet of office space on 200 acres of land that parallel I-270 from Montrose Road to New Mark Commons. The plans call for up to 17 buildings, including the office tower.

The company also is asking the city to create a special zoning category that will allow it to develop the property more densely than any other office park in the city.

Westmont bought an interest in the property in 1979 and formally proposed developing the tract this summer in a meeting with the Rockville City Council, the Planning Commission and the mayor.

Dallas-based EDS Corp., a computer firm, plans to use 60 percent of the office space for a regional headquarters. But the company has warned Rockville officials it will look elsewhere, including Northern Virginia, if development is delayed, Kenney said.

Last week Westmont cleared its first major hurdle when a 13-member advisory committee made up of developers, business executives and residents approved the company's development plan.

The committee, however, called on the commission to develop a plan to ease traffic congestion before it approves the development.

The committee also asked the commission to consider staging development to coincide with improvements to I-270, Montrose Road and Ritchie Parkway. Kenney said Westmont plans to develop the site over 10 to 15 years.

Westmont executive Kenney said his company is attempting to address all citizen concerns. "They said the building was too high so we sent up the balloon. We are trying. We've taken to heart what they've said."