Managers of the 6th Street Marketplace, the troubled retail complex touted as a key to the renewal of downtown Richmond when it opened two years ago, are more bullish than ever about the project's future after a summer surge of conventioneers, festival-goers, beer drinkers and barbecue lovers.

Tens of thousands of people -- drawn to the marketplace by Friday afternoon concerts (and nearby beer trucks), a national rib cook-off, a Baptist convention, fireworks and other events -- helped push June sales at the James Rouse-designed complex to 20 percent above the June 1986 level, officials said.

"We've had a great summer," declared marketplace manager Ted Cosmos. "Now we're looking forward to the Christmas season."

But at the same time, Richmond officials say they are still concerned about the marketplace's direction -- enough to increase dramatically the role that city government will play in the future of the $25 million complex of department stores, shops, restaurants and food stalls.

"The verdict is still out," said Henry L. Marsh III, one of two City Council members who are overseeing a special 6th Street Marketplace study. In mid-July, the city pledged more than $2.5 million in additional financing for the marketplace through 1991.

"There's a growing recognition that the city needs to play a greater role to ensure the success of the marketplace," Marsh added. "Before the marketplace reaches its full potential, there has to be a turnaround. But I also think we'll see some improvement long before then."

Cosmos notes several statistics that he says reflect a rebound of sorts after months of tenant unrest and faltering sales. Merchant sales from January to June of this year jumped 15.7 percent over the same period last year, and in a six-week period this summer, 400,000 people visited the marketplace area, Cosmos said.

In addition, several stores have opened at the marketplace. Meanwhile, Cosmos said he "wholeheartedly" welcomes the city's greater financial stake in the project.

"The city has to be the coach and the cheerleader," Cosmos said.