Southeastern Connecticut’s casino-owning Indian tribes, the Mashantucket Pequots and the Mohegans, focused new attention Friday on their bid to land a third Connecticut casino, announcing that they are re-opening their request-for-proposals process.

The tribes have been vetting plans involving sites at Bradley International Airport in Windsor Locks and in East Hartford and Hartford.

“We know that folks are anxious for this process to move forward, and so are we,” Kevin Brown, the Mohegan chairman, said in a statement. “But as much as we want to get shovels in the ground, we also want to make absolutely certain that we invest hundreds of millions of our own money in the right site.”

“We’ve said from the beginning that we want to build this facility in a place that values the large investment we’re going to make,” Rodney Butler, the Mashantucket chairman, added.

The deadline for the second round of submissions is Oct. 15.

Thereafter, “a set of finalists will be announced and an extensive public engagement campaign will begin in each of the finalist communities,” the tribes said.

Although no municipalities other than the three currently in the running formally have indicated they will respond to the new request for proposals, they may if they wish, Chuck Bunnell, the Mohegan Tribe’s chief of staff, said.

“If someone’s got something that we haven’t looked at, and they want us to look at it, we will,” he said. “We want to do this right.”

The tribes, joint partners in MMCT Venture, are pursuing the third casino out of concern over the impact of MGM Springfield, a $950 million resort casino under construction in Massachusetts.

The project, scheduled for completion in September 2018, is expected to divert jobs and revenue from Foxwoods Resort Casino and Mohegan Sun — and, by extension, the state, which takes 25 percent of the existing casinos’ slot-machine winnings.

Las Vega-based MGM Resorts International, which has sought to block the third-casino effort, blasted the tribes’ announcement Friday.

“This isn’t a process — it’s a sham,” Alan Feldman, an MGM Resorts executive vice president, said in a statement. “It is being run by MMCT, not the state, and MMCT is running it for its own purposes. Deadlines are set, then they’re missed. Towns are added, then subtracted. Unrealistic job numbers are created out of thin air, then thrown around with impunity. We’re told this is a ‘satellite casino,’ then, when information is pried loose, we see renderings of a casino larger than anything in Las Vegas.”

Feldman was referring to the Connecticut Airport Authority’s consideration of plans for a large casino that would have been developed along with a new ground transportation center at Bradley, which the authority operates.

Those plans have been abandoned.

Kevin Dillon, the authority’s executive director, briefly addressed the lingering prospect of a Bradley casino during a meeting this week of the authority’s board of directors.

“He reiterated to the board that the previously submitted site proposals, which included the new ground transportation center and Terminal B, have been withdrawn from consideration. However, the CAA is still interested in pursuing a casino at Bradley Airport, which has 300 acres available outside the terminal,” Alisa Sisic, an authority spokeswoman, wrote in an email.

A week ago, Silver Lane Partners, the group behind the East Hartford proposal, announced a new wrinkle in their plan, which calls for a casino in a former Showcase Cinemas building off Interstate 84.

The partners said they had reached an agreement that would enable them to link the casino to the Radisson Hartford Hotel on the opposite side of the Connecticut River. Shuttles would ferry patrons between the casino and the hotel.

Tony Ravosa, Silver Lane’s managing member, expressed disappointment Friday that the site-selection process was being drawn out.

“The stakes are enormous in terms of potential lost revenue to the state of Connecticut if the tribes — in partnership with the state — fail to respond to the competitive threat posed by the expected opening of MGM Springfield in September 2018,” Ravosa said in a statement.

“The clock is ticking, and MGM’s construction site is bustling with activity," he said in the statement. "If the tribes and state neglect to select and approve a site for the third Connecticut casino in relatively short order, the potential impact on the state budget beginning in 2019 will be both sizable and debilitating.”

Ravosa called for state lawmakers to “play a more assertive role” in the process.

MMCT representatives have reviewed a number of potential sites in Hartford.

b.hallenbeck@theday.com