At a time when local governments are competing fiercely for economic development, a proposed $500 million complex that will generate 15,000 jobs is being greeted like an unwelcomed uncle in Montgomery County, where booming development is fueling unprecedented traffic congestion on county roads.

"Traffic is going to be generated by all that development that will more than saturate I-270, even it is widened to 12 lanes," said Allen Bender, who chairs the Coalition on Sensible Transporation, a group that is suing to block expansion of the interstate.

"Basically, it's too much development with too big an impact on the downtown areas of Rockville and Gaithersburg," added James M. Davis, Rockville's planning director.

The proposed Washingtonian Center development is slated to be the cornerstone of a futuristic "high-tech" city -- rivaling Tysons Corner in size -- in Montgomery County's bustling I-270 corridor.

Despite years of planning, lingering concern over the project's impact prompted the County Council this week to delay rezoning the property until the complex could be studied more closely.

The delay was a frustrating setback for Atlanta-based Ackerman & Co., which had hoped to start construction on a hotel, offices, restaurants and the first of 1,400 homes as early as next year.

But if anything, the council's hesitation illustrates how concern over traffic congestion and eroding confidence in county planning have become the biggest stumbling blocks to growth in Montgomery County.

That point was made most directly by Council Member David L. Scull, who tossed aside a detailed traffic analysis of the complex and asked for an even more detailed "building-by-building" count of cars that will flood county roads as the project builds out.

"I don't think enough information has been made available about the development's impact on roads, the environment or the schools," agreed Robert Sher, president of the Mid-County Civic Assocation, which represents area residents. Ackerman & Co. had filed an application last year to rezone the 211-acre property to a new "mixed-use" zoning category that encourages development of integrated projects on large tracts of land.

The County Council created the classification last year just before approving a sweeping 30-year land-use plan that will transform the area of the county between Rockville and Gaithersburg into a high-tech research and development city with 21,000 houses and 8 million square feet of office space.

Ackerman has proposed building more than 1,400 mid-rise and garden apartments and more than 4.5 million square feet of commercial space on the property. The complex also will include two hotels, a conference center, six restaurants, theaters, a health club and such amenities as an eight-acre lake.

It will flank I-270 on the east and the planned I-370 connector to the Shady Grove Metro Station on the north, and will contain almost half the area's planned growth.

A key element of the new zoning classification requires staging development with road construction so traffic does not inundate the already congested road system.

Robert Metz, a zoning attorney for Ackerman, said the developer met more than 100 times with county planners and transportation experts to work out a detailed staging plan.

Development has been split into two phases that are tied to the construction of six road projects. The first phase of development will be triggered by widening Shady Grove Road from I-270 to Route 28, improving the Shady Grove interchange with I-270 and constructing Omega Drive.

Under the staging plan, Ackerman would be able to start constructing two 200,000-square-foot buildings, a 250-room hotel, a sports and health club and the first of 784 housing units by late 1986.

Completing I-370, widening Fields Road west of I-270 and constructing the Great Seneca Highway would trigger the second phase of development: 750 additional housing units and 2.7 million square feet of commercial and office space. The project is scheduled for completion in 1995.

Officials from Rockville and Gaithersburg have complained that the development is contrary to the "wedges-and-corridors" concept of the region's original 1964 master plan. The two cities were designated in the plan as centers of growth surrounded by low-density development.

"There is a fair amount of office space still available in Gaithersburg, and more is planned. If the development at Shady Grove precedes our development, it could hurt," said Gaithersburg Mayor Bruce Goldensohn.

Rockville planner Davis noted that the complex is slated to contain as much office space as the city's own business district.

Meanwhile, Rockville, recognizing the area's traffic problems, is limiting development on a similar-sized, 200-acre tract to half the density of the Washingtonian center, he said.

"What's being constructed there . . . was never called for in the original master plan," Davis said.

Ackerman attorney Metz said this week that traffic congestion is not a valid reason to deny rezoning for the property. He criticized the council for failing to comprehend the development's staging plan.

"We never have experienced this kind of intensive analysis and investigation anywhere," said Charles S. Ackerman, president of the development company, after the council's decision to delay the rezoning.

"It doesn't ever seem to reach a point of reconciliation, and that's very frustrating," he said.