The Arlington County Board yesterday turned down a developer's third proposal to build an office-and-hotel project on the site of the aging Washington-Lee Shopping Center in South Arlington.

Board members were responding to protests by neighborhood organizations and dozens of residents of the area just west of Fort Myer. However, they acknowledged that their decision might make it easier for a less-attractive, less-well-landscaped office project to be built there.

Barnes Lawson, a spokesman for the Fairfax-based developer, Sequoia Building Corp., said that "it's just a matter of fact" that the board, by denying the company's plan, was virtually guaranteeing that Sequoia or another developer was going to build a less-distinguished office project on the 12-acre site, near the intersection of Arlington and Washington boulevards.

"I don't know what the future project is going to look like, but it could end up looking like Wilson Boulevard" near Rosslyn, said Ray F. Smith, Sequoia's president.

The Sequoia representatives later said that, now that their plan is dead, it is likely that they will come back and propose a four-story office complex almost as large as the one the county board denied in a 5-to-0 vote.

This time, company officials said, the county would have little power to deny it because this plan would conform with current zoning regulations for the area.

Sequoia's proposal, supported by the county planning staff, was to build 500,000 square feet of office space in two terraced buildings ranging from three to eight stories; a 10-story, 250-unit hotel; and a small number of stores.

That proposal was the company's third one, because Sequoia had repeatedly scaled down its plans in the past months in response to residents' complaints that the project was inappropriate for the neighborhood and would cause traffic tie-ups.

Company officials even presented a new, fourth proposal yesterday, scaling down the office buildings and forgoing the stores.

Many residents and shopping center merchants opposed all the plans, even though most praised their landscaping and the company's effort to "buffer" the project from nearby homes.

As pleased neighborhood residents watched, board members gave a long list of the kinds of projects they would like to see in place of Sequoia's plan.

Board member John Milliken, running for reelection next month, said that, ideally, he does not want large office buidings there. Board nember Michael Brunner said he wanted a recreational area, "shops, restaurants, whatever."

Sequoia consultants, who moments before had been acting obsequiously to the board members, smirked, snorted and muttered. "Wishing it won't make it happen," one said under his breath.

"There's no question in my mind the county would have been better off with our first plan," Smith said.