The Reverend Al Sharpton and Olympic long jump record holder Robert Beamon joined thousands of union members at a rally to support a West Side football stadium yesterday, the eve of a crucial vote on the plan.

“This is not about fun at the stadium; this is about jobs at the work site,” said Rev. Sharpton, a new member of the pro-stadium forces led by Mayor Bloomberg and the New York Jets, the NFL franchise that hopes to play its games at the new facility starting in 2009.

The $1.7 billion stadium would be built on a platform over rail yards owned by the Metropolitan Transportation Authority, which was scheduled to vote today on the Jets’ plan and two competing proposals, one from Cablevision, which owns Madison Square Garden and has promised to build housing on the site.

Published reports yesterday said a majority of the 14-member MTA board would vote for the stadium, which would also host the 2012 Olympics if New York were chosen for the Games.

[Mr. Bloomberg’s office issued a statement yesterday from four city officials serving on the MTA board – John Banks III, Susan Kupferman, Mark Lebow, and Mark Page – who said the Jets bid was “superior” and “in the best interests of the MTA and the city.”]

Cablevision, in a letter yesterday to the MTA, called on the agency to disqualify the Jets’ bid because it violated the bidding requirements. “Taken as a whole, the Jets’ value proposition to the MTA is highly contingent and misleading,” said the letter from Cablevision attorney Randy Mastro.

MTA spokesman Thomas Kelly said the agency was preparing a response to the letter. A call to the Jets about Cablevision’s last-minute attempt to scuttle the bid was not immediately returned.

With the Jets promising more than 18,000 construction jobs and 7,000 permanent jobs, building trades unions have been staunch backers of the team’s plan.

Organizers of yesterday’s rally outside the Midtown Manhattan headquarters of the MTA, which runs the nation’s largest mass transit system, estimated the turnout at 20,000. Most wore hats and jackets identifying their union locals and waved flags promoting the city’s 2012 Summer Olympics bid.

“Today we are on the 1-yard line,” said Edward Malloy, president of the Building and Construction Trades Council of Greater New York. “Tomorrow you are taking us into the end zone. Tomorrow we win!”

Jets’ head coach Herman Edwards said, “Your passion is important. It’s very, very important, because passion and belief gets things done.”

Mr. Beamon, who set the Olympic long jump record of 29 feet, 2.5 inches in 1968, said he’d like to see someone try to break the record “right here in Manhattan.”

“I tell you, this is the place,” he said. “The Apple is the place to have the Olympic Games.”

The MTA opened the bidding process for the site on Manhattan’s far West Side earlier this month, one year after city and state officials announced the stadium plan.

Under the Jets’ proposal, the team would provide up to $720 million, with $440 million coming from six developers who would buy excess development rights on the site. Their offer would depend on zoning changes. The state and city would pay $600 million for a platform over the rail yards and a retractable roof.

Cablevision Systems Corp.’s offer of $760 million includes $400 million in cash up front and the rest in a promise to construct a platform over the rail yards. Cablevision’s Madison Square Garden, where the New York Knicks and New York Rangers play home games, is just blocks from the rail yards.