Reston Town Center, the planned community's version of a vintage downtown, opened officially yesterday despite a slumping economy that has left some of its office space unleased.

The fountain at the heart of the center area -- a white marble structure topped by a statue of Mercury, the Greco-Roman god of commerce -- was dedicated amid musical as well as natural fanfare: strong winds and rain threatened to force the dedication inside.

The center, called an urban marketplace by its developers, is expected to house 220,000 square feet of retail space, consisting of 60 shops and restaurants, two 11-story and several mid-rise office buildings, a 14-story, 514-room Hyatt Regency Reston hotel, and an 11-screen Multiplex Cinema.

The hotel and several shops, such as Ann Taylor, Banana Republic and Raleigh's, already have opened and some of the office space is filled. The center was several years in the planning, at a time when the Washington area economy was booming. But the area is now suffering from a sharp drop in home sales, losses of jobs in defense, construction and real estate, and soaring bankruptcies.

"A project this big takes so long to put together, it's impossible to foresee economic trends," said Kenneth P. Wong, senior project manager for Reston Town Center. "We're not immune" from the downturn.

He said leasing of space is "a little shy" of expectations, but that it is doing better than other places. Officials had hoped to lease about 50 percent of the office space by yesterday, but just more than 40 percent was leased, Wong said. But he said 85 percent of retail space has been leased, "right where we hoped to be."

Although speakers yesterday referred to the town center as returning to a bygone era, its brick streets and sidewalks border mostly upscale shops, a more modern phenomenon. Wong said that the center plans to include other stores such as a dry cleaner, an office supply store and a photocopier.

"We don't see this as exclusively a place for big upscale" shops and businesses, Wong said.

Development of the 85-acre downtown site is expected to continue through the 1990s. So far, 20 acres of the first phase have been completed.

The town center was part of the original plan of Reston's founder, Robert E. Simon, who yesterday called the downtown area "fantastic. It's, as you know, the beginning of the grand finale. It's not finished, but it's a perfect step in the right direction."

Reston already has about 12 million square feet of office space, excluding the town center, making it second to Tysons Corner in the amount of office space in a Northern Virginia community.

Plans call for as many as 1,600 apartment and row house units, another hotel, more office buildings and additional parking garages.