When a federal judge in late July stripped the Mashpee Wampanoag tribe of its sovereign reservation, ruling that the US government had mistakenly approved it, the tribe’s plans of opening a $1 billion resort casino in Taunton suffered a major setback.

But the next day, as attention focused on the tribe’s next move, a second federal court ruling involving the Cowlitz tribe in Washington state gave its legal quest renewed hope, providing a potential road map — as if on cue — for a successful appeal.

The ruling shifts the legal landscape for Indian reservations and breathes new life into the tribe’s long-deferred quest for a resort casino, one of at least three planned for Massachusetts. Supporters of casinos want to bring gambling to the southeastern part of the state to fight growing competition from Rhode Island and Connecticut.

“The two rulings are inconsistent, and that gives the Mashpee a chance to get a reversal,’’ said Dennis Whittlesey, a Washington, D.C., lawyer with decades of experience in Indian law.

The divergent rulings center on the interpretation of a controversial Supreme Court ruling in 2009, known as the Carcieri decision. That ruling, which tribes have sharply criticized, seemed to limit eligibility for reservations to tribes that were under federal jurisdiction in 1934, when Congress passed the Indian Reorganization Act.

That would clearly disqualify the Mashpee and the Cowlitz tribes, who are among a handful of tribes that only gained recognition from the federal government in the past 15 years. Nevertheless, the US Department of Interior granted sovereign land to both tribes in recent years, seemingly sidestepping the Carcieri decision to give them casino rights.

With the government’s blessing, the Mashpee have expressed confidence their casino plans would ultimately prevail in court.

The tribe broke ground this spring despite a lawsuit, filed by neighbors to the Taunton casino, challenging the validity of its reservation status.

Government lawyers defending the grant of reservation status to the Mashpee have argued that the 1934 law, which authorized federal authorities to acquire property “for the purpose of providing land for Indians,’’ is ambiguous.

But US District Judge William G. Young rejected that position, siding with plaintiffs who had called for a “plain reading’’ of Carcieri. “With respect, this is not a close call: to find ambiguity here would be to find it everywhere,’’ Young wrote.

Young’s decision was a heavy blow to the Mashpee, and the tribe soon halted construction.

But in its Cowlitz decision, the federal appeals court in Washington, D.C., saw things differently. Consistent with other lower court rulings that have addressed the issue, the court upheld the Interior Department’s determination that the Cowlitz tribe, although not federally recognized until 2002, met the threshold of being under “federal jurisdiction’’ in 1934.

That appeals court ruling, issued July 29, gave the Mashpee’s casino plans new hope.

The appeals court ruling prompted lawyers for the Interior Department to ask Young to reconsider the ruling that had hurt the Mashpee’s chances. In late August, they argued that the logic in the Cowlitz decision applied equally to the Mashpee’s situation. Young was mistaken, they argued, when he equated “federal recognition’’ with “federal jurisdiction.’’

The Mashpee applauded the government’s quick intervention, noting that Young’s decision had left them without sovereign land.

"We’ve been on our land for thousands of years, and all we seek is the right to exist here as a sovereign people,’’ said Cedric Cromwell, the Mashpee tribal council’s chairman. “It was promised to us soon after the first Pilgrims arrived, and it’s a promise we hope the courts will honor.’’

Tribal officials declined to comment on the Cowlitz decision.

Many legal experts expressed surprise over the court’s decision to strip the Mashpee tribe of its reservation, saying it could be eventually overturned.

“That was a surprising ruling,’’ Whittlesey said. “I really thought it would go the other way. But when the tribe appeals, I’m sure the Cowlitz case will be very much a part of it.’’

But Adam Bond, a lawyer for the Taunton property owners, said the Cowlitz and Mashpee cases are fundamentally different because the Cowlitz had some interactions with the federal government in the 19th century, while the Mashpee had none.

“The Mashpee were under colonial and state jurisdiction, not federal,’’ Bond said.

Some of the controversy appears to stem from the Carcieri ruling, which curtailed the government’s authority to designate reservation land for tribes that only recently gained federal recognition, even though they say they never ceased to exist as tribes. Robert Clinton, a law professor at Arizona State University, called the Carcieri decision “poorly reasoned, ill considered, and badly decided.’’

“It was apparent that Congress intended for tribes recognized at any time to have reservations,’’ he said. “These two cases are the fallout from Carcieri.’’

The Mashpee had hoped to open the state’s first full-scale casino next June, but now the tribe seems likely to face a lengthy delay, with its chances hinging on the interpretation of a Depression-era law.

Sean P. Murphy can be reached at smurphy@globe.com. Follow him on Twitter @spmurphyboston.