A City Council member from Brooklyn, Letitia James, said yesterday that her constituents are “jumping up and down in joy” after a Manhattan-based development firm made a bid to block a real estate mogul, Bruce Ratner, from erecting a high-rise hub on a site in Ms. James’s district that is owned by the Metropolitan Transportation Authority.

Earlier this week, Forest City Ratner submitted a proposal to build six skyscrapers, rising as high as 60 stories, as well as a pro-basketball arena for the New Jersey Nets and other buildings in the Atlantic Yards portion of downtown Brooklyn. The footprint of Mr. Ratner’s proposed development would extend far beyond the 8.5-acre rail yard owned by the MTA and would require the eviction of hundreds of tenants who live on the surrounding blocks.

Neighborhood activists, in alliance with Ms. James and a handful of other local politicians, have waged a two-year battle to thwart Mr. Ratner’s project. Others, including Mayor Bloomberg, have hailed the Ratner plan as a welcome investment in the future of the city’s most populous borough. On Wednesday, Mr. Ratner’s opponents gained a powerful ally in Extell Development Company, which submitted a competing bid for the MTA site.

Ms. James, a Democrat, charged that Mr. Ratner and his associates want “to build towers in the sky as a monument to themselves.” Extell’s bid, she told The New York Sun, is “sensitive and considerate.”

A spokesman for a group that has opposed the Ratner project, Develop Don’t Destroy, expressed a “cautiously optimistic” attitude toward the Extell proposal at a press conference at City Hall yesterday afternoon.

Afterwards, Daniel Goldstein, the spokesman, and a dozen other neighborhood activists headed to Joe’s Shanghai restaurant in Chinatown for a celebratory dim sum luncheon.

“We’re excited – and we have all right to be,” Mr. Goldstein said, adding that his group had met with Extell planners last month and the firm incorporated neighborhood activists’ suggestions into its proposal.

Meanwhile, powerful politicians, including Mr. Bloomberg and the Brooklyn borough president, Marty Markowitz, rallied behind Mr. Ratner anew yesterday.

“The mayor supports the Ratner plan because it will create thousands of new jobs, bring a major league sports franchise back to Brooklyn, and build more than 4,000 units of housing,” a mayoral spokesman, Jordan Barowitz, told the Sun. In addition to creating thousands of units of housing, Mr. Ratner has said his plan will create 1.9 million feet of office space on the 21-acre plot.

Mr. Markowitz blasted the Extell proposal in a statement.

“The Extell proposal may benefit the small number of people who are opposed to the Ratner plan, but it certainly doesn’t benefit most Brooklynites,” the borough president said. “Where’s the affordable housing? Where’s the job outreach for the community?”

An Extell spokesman, Robert Liff, said the company’s plan would create 1,940 units of housing, 30% of which would be subsidized rental units. He said the Extell plan would also create 116,000 square feet of retail space and 170,000 square feet of parkland, and would set aside 73,000 square feet for a community center or school. No building would rise above 28 stories.

Mr. Liff also said that, unlike the Ratner plan, the Extell proposal would not uproot a single tenant or small business in the surrounding neighborhoods.

Mr. Ratner’s plan, which would require the city to seize nearby properties from existing owners, received a boost late last month when the U.S. Supreme Court adopted an expansive interpretation of local governments’ powers of eminent domain. But the Ratner-Extell bidding war could ultimately hinge on the amount of money each entrant pledges to pay the MTA for the rail yard.

Mr. Liff would not say how much Extell has offered the transportation authority. He asked, rhetorically: “Is Ratner releasing how much they bid?” A Ratner spokesman, Barry Baum, declined to comment.

The director of the watchdog group New York Civic, Henry Stern, said the Extell bid might be a “last-minute spoiler which provides a few extra bucks up front” – but less income for the MTA over the long term.

Extell’s proposal comes two months after Mr. Goldstein’s group sent letters to approximately 100 developers urging them to compete with Mr. Ratner for control of the MTA site.

Mr. Liff said his firm is stunned that other companies are not vying for the rights to build on the Atlantic Yards.

“This is the prime development site not only in Brooklyn, but, outside of the West Side of Manhattan, the prime development site in the city,” Mr. Liff said. “We’re surprised that other developers haven’t bid on this property.”