A proposal to legalize slot machines at the state's four race tracks was dealt a serious wound Wednesday when House Speaker Sal DiMasi came out against the bill.

State Sen. James Timilty said opposition from House leadership likely sounds `` a death knell'' for slot machines.

He said even if the bill passes the House, leadership opposition means it will not get the two-thirds support needed to override a promised veto by Gov. Mitt Romney.

The bill allowing 2,000 slot machines at race tracks, including Plainridge Racecourse in Plainville, has already passed the Senate.

State Rep. Richard Ross, R-Wrentham, a strong supporter of slot machines, was a little more optimistic than Timilty. Ross said he and other supporters have sent a letter to House colleagues reminding them of the economic benefits of slot machines.

Massachusetts residents, he said, are spending $831 million a year at Connecticut casinos and $197 million on Rhode Island slot machines.

Legalizing slot machines would raise $500 million a year in tax revenue for Massachusetts, he said.

Still, Ross said DiMasi's opposition is not helpful.

`` I think its not good news. I just wish he would more openly embrace the revenue side of this for the commonwealth,'' he said.

The district Ross represents includes Plainville, home to Plainridge Racecourse.

Ross said another odd development in the issue is that the Senate Wednesday passed a one-year extension for simulcasting at tracks.

Simulcasting was suppose to be coupled with slots into one bill, so the signs are that the Senate is convinced slots will not pass the House.

DiMasi told the Greater Boston Chamber of Commerce Wednesday that he believes the slot machine bill will fail.

He said expanded gambling will come with high social costs and will not raise the predicted amounts of revenue. The speaker did say he would support a bill to extend simulcasting, but also said he considers racing a `` dying industry.''

While DiMasi's statement was worrisome to supporters of race tracks, it was welcomed by critics of greyhound racing.

The Committee to Protect Dogs, which wants to end greyhound racing and opposes slots because they would help keep tracks open, praised the speaker.

`` We applaud Speaker DiMasi for standing up to wealthy dog track owners and opposing'' slot machines, said Christine Dorchak, chairwoman of the committee.