After an all-day sales blitz by developers and county planners, the Montgomery County Council gave final approval yesterday to the $500 million Washingtonian Center, which promoters say will be the "shining centerpiece" of future Shady Grove West development.

The council voted 5 to 2 in favor of the zoning for the project, with members Scott Fosler and David Scull opposing it. Voting in favor of the project were Michael Gudis, William Hanna, Neal Potter, Rose Crenca and Esther Gelman.

"I've had my faith lifted," punned Crenca, and Gelman told developers she hoped the mixed-use minicity would be "a real jewel in the crown" of upcounty growth.

As envisioned by developers, the finished center would feature two hotels, a conference center, retail outlets, a health club, a large public park and lake and 1,400 apartments.

The triangular site, bounded by Interstate 270 to the east, Fields Road to the south and the future I-370 extension to the north, would be sectioned thematically with the apartments on the western side of the tract, the hotel and higher-density commercial area in the center and the lake and park as a buffer against the interstate.

The Washingtonian Tower, a high-rise currently on the site, will remain, but a motel and golf course there will be eliminated.

Although the proposal had already passed muster with county planners and zoning board examiners, final approval by the council had been delayed since Oct. 8 by intensifying debate over traffic congestion in the I-270 corridor.

Promoters of the Washingtonian project had applied to have the more than 200-acre tract rezoned as "MXPD," a classification created by the council last year to encourage integrated commercial and residential development of major sites.

The new mixed-use zoning requires careful "staging" to prevent development from outpacing construction of roads and public facilities.

Citizen groups such as the Coalition on Sensible Transportation and the Mid-County Civic Association have argued that the Washingtonian Center and the proposed research and development clusters nearby would strangle the already overloaded highways.

Gelman said the new classification should meet those fears.

"Of all the things I've heard or seen, the thing that's different today is that we can tie building permits to road construction," she said.

Robert McGarry, director of the Montgomery County Department of Transportation testified after conducting a traffic study requested by the council last month that all highways keyed to the Washingtonian development would be under construction by 1988.

And backers of the center hauled out chart after chart intended to demonstrate that the project would have minimal, or at least acceptable, impact on local traffic.

Edward Y. Papazian, traffic engineering consultant for the developers, testified that the development will not add any cars to local traffic for several years; and that of the 750 estimated cars coming into the Washingtonian Center daily by 1990, the majority will be "counterflow" traffic, moving northward, or in the opposite direction of most traffic, along I-270 at morning rush hour.

Papazian and McGarry also pointed to the widening of I-270 as a factor in reducing traffic in the area, and Papazian suggested that some short-trip traffic that now uses I-270 would have transferred to the proposed Great Seneca Highway by the end of the decade.

As displayed in the promoters' slide show, the center is a combination Montgomery Village and small-scale Harborplace, primarily designed for what builders Crow & Terwiliger have called the "YMCAs" -- young, married, childless achievers.

Phase 1 of Washingtonian Center construction, which would begin next year, would create more than 1.8 million square feet, including 1.4 million square feet of office space, a hotel and nearly 800 garden and midrise apartments.