The fight over the Metropolitan Transportation Authority’s rail yard in downtown Brooklyn turned ugly yesterday morning as supporters and opponents of developer Bruce Ratner’s bid for the site exchanged bitter, profanity-laden personal attacks during a public meeting at the MTA’s Midtown headquarters.

When a spokesman for the anti-Ratner coalition Develop Don’t Destroy, Daniel Goldstein, rose to speak at the MTA real estate committee’s monthly meeting, the treasurer of the pro-Ratner group BUILD, Jasmin Miller, muttered: “Trust fund baby.” Mr. Goldstein wheeled around, looked Ms. Miller in the eye, and unleashed an expletive.

Members of both groups were still fuming as they congregated on a Madison Avenue sidewalk after the meeting.

“What I do for a living is not the issue here,” Mr. Goldstein, a freelance Web designer, said.

Just steps away, the president of BUILD – the group’s full name is Brooklyn United for Innovative Local Development – James Caldwell, cast the conflict over the 8.4-acre Vanderbilt Yards site in racial terms.

“If this thing doesn’t come out in favor of Ratner, it would be a conspiracy against blacks,” Mr. Caldwell said.

He said Mr. Ratner, a 60-year-old white who served in the Koch administration, “is like an angel sent from God” because the developer is willing to negotiate with local black leaders.

The Vanderbilt Yards sale did not appear on the real estate committee’s agenda, according to its chairwoman, Nancy Shevell Blakeman, who said the committee was breaking with long-established precedent by allowing public comment on a non-agenda item.

Another member of the MTA board, Barry Feinstein, told the activists: “You’re talking to people who don’t have any details about the two proposals.”

But the 17 members of the authority’s board, including the 12 who sit on the real estate committee, are in for a crash course on the Vanderbilt Yards debate. They received background briefings from MTA staff yesterday and today, and the full board could cast a final vote on the competing bids for the rail yard site as early as tomorrow morning.

The Ratner plan calls for a high-rise urban hub and a basketball arena for the New Jersey Nets on a 21-acre expanse. The developer has already purchased most of the land adjacent to the rail yard, while city and state officials have said they will use their power of eminent domain to seize about 20 remaining parcels from residents and businesses that have not agreed to sell their properties to Mr. Ratner’s firm.

A rival bidder, Extell Development Company, has submitted a competing proposal to build a smaller-scale project within the confines of the MTA owned rail yard.

Mr. Ratner is offering the MTA less cash for the site: $50 million, compared with Extell’s $150 million cash bid. And Mr. Ratner’s bid relies more heavily on public money: Governor Pataki and Mayor Bloomberg have pledged $200 million in aid for the Ratner project, while Extell says it would need $150 million in city and state funds.

The BUILD group favors the Ratner plan, however, in part because it would provide more housing for low-income and middle-class residents: 3,000 “affordable” units, versus Extell’s promise of 573 affordable units.

As activists waited inside the MTA headquarters before being allowed into the committee meeting, the fifth floor hallway was as racially segregated as an Alabama bus in the 1950s. When one white Park Slope resident ventured over toward the corner where several black BUILD volunteers stood, he received an earful from build’s small business director, Michael West.

“When you reject the Ratner project and embrace the Extell project, you’re saying you don’t care about the 55% unemployment in the black community,” Mr. West said. Mr. Ratner has said his firm’s plan would create 15,000 construction jobs and 7,500 permanent jobs.

According to documents released Friday by the MTA, Extell has promised that 20% of construction work on its project will go to businesses owned by minorities and women. An Extell spokesman, Robert Liff, said the firm’s pledge accords with the guidelines set forth by several community activists, including members of Mr. Goldstein’s group, in meetings with Extell officials. But that is less than the 30% of construction contract dollars that Mr. Ratner promised his firm would award to businesses owned by members of minority groups and women, under an agreement signed last month by the developer and a predominantly black group of Brooklyn leaders, which included Mr. Caldwell.

Also on Friday, a Democratic state assemblyman from Park Slope, James Brennan, and a Democratic City Council member from Brooklyn Heights, David Yassky, sent a letter to the MTA board urging members to stall consideration of the Vanderbilt Yards bids, arguing that both the Extell and Ratner plans are “too big.”

Even if the MTA board does vote on the bids tomorrow, that might not be the last word on the future of Vanderbilt Yards. Before the Ratner project or the Extell plan can receive state subsidies, it would need the approval of all three members of the state’s Public Authorities Control Board: Mr. Pataki; the state Senate majority leader, Joseph Bruno, and the speaker of the state Assembly, Sheldon Silver. Activists on both sides said they are closely watching Mr. Silver, who last month blocked the Jets stadium plan on the West Side because it would have created competition for the rebuilding effort in his Lower Manhattan district. Also last month, about 20 members of Mr. Goldstein’s group trekked to Albany to lobby Mr. Silver’s staff on the Vanderbilt Yards issue. A Silver spokesman, Charles Carrier, said the speaker had no comment on the Ratner and Extell proposals yesterday.