Hartford — With five weeks left in the General Assembly’s current session, the Mashantucket Pequot and Mohegan tribes claimed Wednesday the tide has turned in favor of their bid for a third Connecticut casino.

Still, the likelihood that the necessary legislation will pass remained hard to gauge.

While Sen. Cathy Osten, the Sprague Democrat whose district includes Foxwoods Resort Casino and Mohegan Sun, insisted the Senate would support a bill sanctioning the tribes’ plan, the speaker of the House of Representatives, Joe Aresimowicz, a Berlin Democrat, told reporters the third-casino matter likely will be decided during budget deliberations.

The session is scheduled to conclude June 7.

On Wednesday morning, some three dozen of the tribes’ southeastern Connecticut casino employees rode buses to the Capitol, where they planned to lobby lawmakers considering both the bill that would grant the tribes the right to build a “satellite” casino on nontribal land in East Windsor, and an alternative measure that would establish a competitive-bidding process among casino operators.

The latter bill would require future legislative approval of an actual casino.

“We’ve got momentum now,” Kevin Brown, the Mohegan tribal chairman, said at a news conference outside the Legislative Office Building, which is attached to the Capitol. “It’s apparent that Senate Bill 957 is the right bill. No other bill gives certainty to the state of Connecticut. If we build in Connecticut, there’s certainty that the 25 percent of slots revenues we pay the state will remain.”

The payments are contingent on the tribes continuing to enjoy the exclusive right to provide casino gaming in the state.

MGM Resorts International, the operator that’s building a $950 million resort casino in Springfield, Mass., 15 miles north of East Windsor, points to a legal opinion in which state Attorney General George Jepsen said the bill favoring the tribes could jeopardize the state’s revenue-sharing agreements with them.

The tribes have said they will continue making the payments if Bill 957 is enacted.

Implementation of the bill would be contingent on the U.S. Bureau of Indian Affairs’ approval of amendments to the tribes’ agreements with the state, Brown said. The tribes expect to receive preliminary approval shortly.

Brown and Rodney Butler, the Mashantucket chairman, spoke to reporters with the casino employees standing behind them. They said an East Windsor casino could “recapture” half of the more than 9,000 direct and indirect jobs that otherwise could be lost when MGM Springfield opens next year, according to estimates.

“Our jobs are important to us, to our families and to our communities,” said Anne Sanders of Waterford, a 13-year Mohegan Sun employee.

Don MacPhee, a member of United Auto Workers Local 2121, the union representing some 1,400 table-games dealers at Foxwoods, said workers at the casino “have an awareness” of the impact the Springfield casino could have on their job security. He said he’s lived through “five or six” rounds of layoffs over the last eight years.

Osten said she was confident the Senate would vote for 957, if it gets the chance.

“I’ve got the votes,” she said. “It’s about jobs.”

The Senate referred the bill Wednesday to the Appropriations Committee, which Osten and Sen. Paul Formica, an East Lyme Republican, co-chair along with Rep. Toni Walker, a New Haven Democrat. Osten declined to predict how the bill would fare in the committee or the House, should it come to a vote there, or whether Gov. Dannel P. Malloy would sign it into law if it reaches his desk.

Soon after the tribes’ news conference, an MGM executive spoke inside the Legislative Office Building.

“An open, competitive process is the only way to go,” Uri Clinton, senior vice president and legal counsel, told reporters. “It’s the only way for the state to maximize the benefits of a third casino.”

He said such operators as Caesars Entertainment and Pinnacle Gaming have expressed interest in pursuing a project in southwestern Connecticut as a way to tap the New York City market. MGM also has considered such a project.

Asked about the impact an East Windsor casino would have on MGM Springfield, Clinton said it was hard to say because the size of the East Windsor facility is unknown.

“It’s a theater they’re renovating,” he said.

The tribes have signed a development agreement with East Windsor officials, and propose to build a $300 million facility on a site now occupied by a vacant Showcase Cinemas building. They plan to raze the building and erect a new structure.

“We like our own competitive position,” Clinton said, adding, “It (East Windsor) would be competition.”

He suggested the tribes’ claim to momentum was bravado.

“I don’t believe they think momentum’s on their side. If they did, they would not be up here saying they’re going to be putting on a full-court press,” he said.

b.hallenbeck@theday.com