A Montgomery County hearing examiner, in a major rezoning decision, has approved a proposed $500 million complex of office buildings, hotels, stores and homes slated for development as part of a futuristic, high-tech corridor city along heavily congested I-270 south of Gaithersburg.

In a 124-page opinion released yesterday, Martin Klauber declared that the "The Washingtonian Center," which Rockville and Gaithersburg officials have said will overload already congested roads, met all requirements of a new zoning category. That category is designed to foster developments on large tracts of land that integrate houses, offices and stores with public facilities and open space.

The Atlanta-based Ackerman & Co., which has built office buildings in Baltimore's Inner Harbor, filed an application last year to rezone 211 acres surrounding the Washingtonian hotel, golf course and country club adjacent to I-270 at Shady Grove Road.

The hearing examiner's opinion, endorsing a change in zoning from a mix of commercial, residential and office uses to the county's new Mixed Use Planned Development (MXPD) zone, clears the way for final action by the County Council. The council is slated to take up the issue Tuesday.

Klauber said the project, the first to be conditionally approved under the MXPD zone, involves one of the "most intricate and innovative" rezonings in county history.

The council created the zoning classification last year in anticipation of approving a sweeping 30-year land use master plan for the 2,000-acre wedge-shaped tract of land between Rockville and Gaithersburg, just west of I-270.

The plan, approved last December, will transform an area of mostly rolling farmland, known as Shady Grove West, into a research and development village with 21,000 houses, 8 million square feet of office space and 30,000 new jobs.

The Washingtonian Center, a key element of the plan, has been designated as the northern gateway because it is flanked by I-270 to the east and the planned I-370 highway to the north.

Ackerman has proposed building almost 1,500 mid-rise and garden apartments and more than 4.5 million square feet of commercial space on the property. The development will include two hotels, a conference center, six restaurants, theaters, a health club and a 30-acre lake.

Public hearings were held on the zoning application last January at which officials from Rockville and Gaithersburg protested the levels of traffic congestion the development would cause.

Traffic is taken into consideration under the new zoning, Klauber said, since development will be staged in two phases based on the construction of six critical roads in the region.

The zoning category requires developers to devote 40 percent of the property to open space and limits parking to underground structures. The company will also donate land and help pay for I-370, according to the opinion.

By late next year, Ackerman plans to begin the first phase of construction on two 200,000-square-foot buildings, a 250-room hotel, a sports and health club and an eight-acre lake. At the same time, construction will begin on 784 dwelling units at a rate of 300 units a year, Klauber said.