One of the 3,200 slot machines at work at Maryland Live! Casino in Hanover, Md. (Mark Gail/THE WASHINGTON POST)

A renewed bid to put a casino in Prince George’s County collapsed in stunning fashion Wednesday as a high-profile work group launched by Gov. Martin O’Malley failed to agree on a larger plan to expand gambling in Maryland.

The development — which abruptly cut short growing momentum for a Las Vegas-style facility at National Harbor — all but ensures that there will not be a special legislative session that O’Malley (D) had advertised for the week of July 9.

Members of the work group said they agreed on several facets of a proposal, including allowing table games such as blackjack and roulette, at the state’s five existing slots sites. But three members of the group — all members of the House of Delegates — balked at the notion of adding a sixth casino.

The group’s other eight members — including three state senators — supported the full proposal, which legislative analysts said would boost the state’s share of gaming revenue by $223 million a year. Most of those eight members, however, were not willing to move forward without a Prince George’s site in the mix.

O’Malley expressed bewilderment at the turn of events, telling reporters he thought there was “broad consensus” among the group, which also included members of his administration and a private-sector financial services executive.

“For some reason, suddenly the House decided they did not want to share on that consensus for reasons that don’t make a whole lot of sense to me,” O’Malley said. “And so I can’t entirely explain it to you. I’m looking forward to hearing back from the speaker of the house sometime.”

Aides said Speaker Michael E. Busch (D-Anne Arundel), who appointed the House members and met with them Wednesday, was not available to reporters after the meeting.

Bringing a high-end casino to Prince George’s had become a priority for County Executive Rushern L. Baker III (D), and prospects seemed to be improving as recently as last week. The developers of National Harbor announced that MGM Resorts International, one of the world’s largest gaming companies, would operate a casino if it were given a favorable tax rate.

In a statement, Baker said he was disappointed, but hopeful that legislative leaders would still reach a deal in time for a summer special session.

Delegates on the work group said they were wary of part of the plan that allowed casino owners, including a new one in Prince George’s, to keep a larger share of slots proceeds than under existing law. Supporters said that was necessary to compensate owners for the additional competition that would come with a sixth casino.

But Del. Sheila Hixson (D-Montgomery) argued that a tax cut for casino operators was difficult to stomach so soon after the legislature had raised income taxes on six-figure earners in Maryland.

Hixson, chairwoman of the Ways and Means Committee, which has jurisdiction over gaming issues, said she had always believed that lawmakers should allow the five casinos they authorized in 2007 to get up and running before adding a sixth location.

That, too, was the view of the Cordish Cos., which opened the state’s largest casino, Maryland Live!, this month in Anne Arundel County. Cordish officials had waged a vigorous lobbying campaign against new competition.

Joe Weinberg, managing partner of the company, said Wednesday that an expansion now would be “premature and not in the best interest of the state.”

“We appreciate the seriousness with which the work group approached its duties,” Weinberg said.

O’Malley officials and senators on the work group characterized the collapse as a lost opportunity. They had been scrambling to craft a plan in time for it to go on the November ballot. Any major gambling expansion in Maryland requires both legislative and voter approval. The next opportunity for the issue to appear before voters would be 2014.

“I’m disappointed that the people won’t be able to vote on this,” said Sen. Douglas J.J. Peters (D-Prince George’s). “I’m disappointed that we won’t have a new revenue source. ... I’m disappointed that we won’t have the new jobs.”

The definition of what would constitute a “consensus” of the work group was never made explicit as it deliberated during recent weeks. It was clear, however, that the views of House members would be given great deference.

On the final night of this year’s 90-day legislative session, a Senate-backed gambling bill with similar provisions failed in the House after becoming tangled up in negotiations over a package of revenue measures that both chambers supported.

O’Malley sought to resume consideration of both of those issues in separate special sessions. Last month, lawmakers completed a three-day session on the revenue measures.

Aides said it is possible — but highly unlikely — that O’Malley could still call a second special session on gaming. But they said it would require some reason to believe the outcome would be different in the House than Wednesday’s events suggested.

Opponents of a Prince George’s casino said they were glad the issue seems to have gone away, at least for now.

Del. Melony G. Griffith (D-Prince George’s) who has clashed repeatedly with Baker over gaming, said she prefers other forms of economic development for the county and thought a delay could be positive.

“This means that time will be provided for clear and thoughtful consideration of several economic development proposals,” said Griffith, who has urged Baker to focus more attention on expansion of the health-care industry in the county.

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Staff writer Miranda Spivack contributed to this report.