An Arlington-based development firm revealed plans yesterday for a $200 million complex of office and residential buildings spanning two blocks in the heart of Ballston, a project that county officials said is one of the most ambitious proposed for the rapidly developing area around the Ballston Metro station near I-66 and Glebe Road.

The proposed mixed-use office-residential-retail project, to be called Stafford Place at Ballston, includes four 11-story office buildings and two 21-story residential buildings on 5.6 acres bounded by Wilson Boulevard, N. Ninth, N. Stuart and N. Randolph streets.

It is expected to provide a key link in the redevelopment of central Arlington's Ballston area.

Since the coming of the Metro station in 1979, Ballston has changed from a modest residential and low-rise commercial neighborhood to the site of more than 30 new residential and office-retail developments containing millions of square feet and giving the area a reputation as an increasingly upscale neighborhood.

Among the other major projects approved in the area's multimillion- dollar high-rise building boom and now in various stages of construction are hundreds of town-house units; the May Co.'s transformation of the Parkington Shopping Center into Ballston Common; Oliver T. Carr Co.'s development of Ballston Plaza, a mixed-use project on nine acres that includes three high-rise office buildings, two high-rise apartment buildings and clusters of town houses; and Ballston Station, an office-residential complex and residential buildings with hundreds of rental and condominium units.

Stafford Place Associates I and II, a limited partnership headed by Arlington businessman Paul Cali, is scheduled to submit plans to the county next week for the mixed-use project. Cali said it took six years to assemble the land, involving negotiations with 26 different landowners.

"It's the kind of thing the county is looking for to get things rolling in that area," said Gary Kirkbride, chief of the county's planning section.

He said the project is the first to take advantage of a new county high-rise zoning category adopted to encourage revitalization of the Ballston area.

The proposed development will link several key projects now underway or proposed for the Ballston area, which the county is promoting as the "new downtown" for Arlington, according to Thomas C. Parker, chief of the county's economic development division.

The project would be connected by an enclosed pedestrian walkway across Wilson Boulevard to the Ballston Common shopping center. On the other side, it would be connected by another walkway to a mixed-use project scheduled to be built by Guiseppe Cecchi's International Developers Inc., which owns the rights to develop the space above the Ballston Metro stop.

"This is the next key piece in Ballston's renaissance from Ballston Common to the Metro station," said Martin D. Walsh, the developers' attorney.

"I equate this project with Baltimore's Harborplace," said John Bernard, president of the Ballston-Virginia Square Civic Association. "Eventually, it will be a showpiece and a benefit to the whole area."

Bernard said the civic association will meet soon with the developers to learn details of the project, and he predicted little neighborhood opposition to the proposal because of Cali's association with the Ballston Partnership.

The partnership is a consortium of about 75 developers, civic leaders and county officials formed earlier this year to help coordinate quality development of the roughly 200 acres that compose Ballston proper.

Cali, who said he expects the County Board to approve the project this fall, said he plans to begin construction early next year. The project would be built in phases over a five-year period.

Its plans include about 2,000 underground parking spaces, almost 800,000 square feet of office space, 108,000 square feet of residential floor space, 81,000 square feet of commercial floor space and 15,000 square feet of restaurant floor space. A large atrium will connect two of the buildings.

Cali said no decision has been made on whether the 621 planned residential units would be rental or condominium.

Stafford Place is the second major proposed project unveiled for the Ballston area this week. The Radnor Corp., a real estate subsidiary of Sun Co. Inc. of Philadelphia, one of the nation's major oil companies, has announced plans to develop an 800,000 square foot high-rise office and residential complex on another block near the Ballston Metro station.

That block is bounded by Glebe Road, Wilson Boulevard, Fairfax Drive and N. Vermont and N. Taylor streets. Some of the properties on that block, however, have not yet been purchased.

Several shop owners on the two blocks assembled by Cali said yesterday that they are uncertain where they will relocate.

However, they seemed resigned to the idea that the future direction of Ballston development is up.

A sign outside the Sleep Shop announced, "After 84 Years! Going Out of Business." Coowner Kathryn Long said the mix of residential and office buildinghs should 1/2revent the area from becoming a place used only in the day.

"The county realized that what happens in Rosslyn is that, with just offices, at night it just folds up. I think they're really trying to prevent that here, and it's a good thing."