The office of Attorney General George Jepsen reacted cooly Friday to a lobbying effort Thursday by the Mashantucket Pequot and Mohegan tribal nations to address legal issues around their push for permission to jointly develop Connecticut’s first casino off tribal lands.

In a letter delivered to legislative leaders and other officials, the tribes seemed to guarantee the continued payment of revenue sharing under a longstanding deal with the state that Jepsen’s office warned could be jeopardized by casino expansion. But Jepsen’s office saw nothing new.

“To the extent the tribes’ letter is intended to articulate a new or different commitment than what has been publicly discussed to date, we would need substantially more detail to venture any opinion concerning it,” said Jaclyn Falkowski, a spokeswoman for Jepsen.

The tribes had no immediate comment.

The tribes chairmen, Kevin Brown of the Mohegans and Rodney Butler of the Pequots, wrote in their letter: “With the development of a third casino operated jointly by Mohegan and Pequot, we are committed to guaranteeing our existing slot revenue arrangement with the State and are proposing compact amendments that will ensure those revenue streams are preserved.”

But that commitment is nothing new, the chairmen acknowledged, since authorization to build the casino off I-91 in East Windsor already is conditional: If the Bureau of Indian Affairs finds expansion would invalidate existing compacts or a related agreement about slots revenue, the new casino would not go forward.

Under memoranda of understanding, the state permitted the tribal casinos the exclusive right to offer video slot machines in return for 25 percent of the gross revenue for slots. That was worth more than $260 million to Connecticut last year.

The tribes, which compete against each other with their Foxwoods and Mohegan Sun casinos, want the new jointly owned casino to maintain market share in the face of competition coming in 2018 from a casino resort in Springfield being developed by MGM Resorts International.

MGM has heavily lobbied against the tribes and promised to tie up the project in court. MGM says awarding the right to a third casino to the tribes without an open process would violate the equal protection clause of the Constitution.

The tribes counter that the award would be defensible as being in the public’s interest: If Connecticut is opened to other casino interests, the tribes lose their exclusivity, and the state loses its claim on 25 percent of the slots revenue at Foxwoods and Mohegan Sun.