D.C. Mayor Anthony A. Williams said yesterday that he opposes putting a baseball stadium on the eastern side of Mount Vernon Square, the most expensive and politically sensitive of five sites that officials had under consideration.

Williams (D), who met with Major League Baseball officials Tuesday, has long expressed reservations about a stadium at Mount Vernon Square because of the high cost of land there. A report by stadium consultants last year put the price as high as $542 million -- about $100 million more than any other site.

The mayor said in an interview yesterday that the other four sites, including two that also are near downtown, remain under active consideration as city officials work to assemble a stadium proposal for baseball officials by mid-March.

"It's really not workable," Williams said of Mount Vernon Square.

Bobby Goldwater, president of the D.C. Sports and Entertainment Commission, said Mount Vernon Square is still being studied but added, "There are other sites that seem to offer more to baseball and the District."

The mayor's comments echoed the sentiments of several D.C. Council members, including Chairman Linda W. Cropp (D), who was in the delegation that met with baseball officials this week.

She and others have argued that Mount Vernon Square, which is in Northwest Washington near the new convention center that is scheduled to open in March, has enough stimulus to ensure rapid development over the next several years. Cropp said the city government's investment in a stadium, which the mayor has said could reach $300 million, would be better spent bringing economic development to a more sluggish area.

"I was never in favor of Mount Vernon," she said. "It was always off the table for me. . . . All the other sites are possible and even very exciting."

Two of the remaining sites are near downtown: the new Metro stop under construction at New York Avenue and a site near Union Station, just north of Massachusetts Avenue. A third site is on the Anacostia River waterfront, near South Capitol Street. The fourth is just north of the existing Robert F. Kennedy Memorial Stadium in Northeast Washington.

A consultants' report commissioned by city officials and one of the possible team ownership groups estimated the cost of a new stadium on the RFK site at $342 million and at the other remaining sites at $411 million to $436 million.

City officials are seeking to settle on a single site and to assemble a financing package that does not use any existing city revenue. Williams said the city's share of construction costs could be paid for using taxes and fees raised at a new ballpark or from development spurred in the immediate vicinity.

The team owners or some other private venture would pay the rest.

The District is competing with Northern Virginia, Portland, Ore., and other areas seeking to become the new home of the Montreal Expos, which Major League Baseball plans to move for the 2004 season.

Baseball officials would like to make a decision before the All-Star Game in July.

Lydia Goring, whose Advisory Neighborhood Commission district includes the Mount Vernon site, reacted with glee when told of the mayor's comments. "Yes!" she said.