PHOENIX - A federal appeals court gave opponents of a casino near Glendale new hope it might be legally blocked.

In a ruling Monday, the 9th U.S. Circuit Court of Appeals said it may very well be that the site owned by the Tohono O'odham Nation, while in an unincorporated area, is "within the corporate limits of any city or town." That's because the parcel is on a county island, surrounded by land within Glendale.

That question is crucial.

The 1986 law that permits the tribe to buy the land and have it become part of the reservation requires it be outside the corporate limits of any city.

If the 54-acre parcel is "within" Glendale's corporate limits, then there can be no reservation status. And without reservation status, the tribe cannot operate a casino there.

Monday's ruling does not decide the issue one way or the other. Appellate Judge Margaret McKeown, writing for the court, said Arizona law on the question can be read either way.

Instead the judges directed the interior secretary, who had concluded the land was not "within" Glendale, to take another look.

But while two of the judges said the question is unclear, the third judge on the panel, Randy Smith, said he had no doubts. Smith said the land is definitely within Glendale's limits, precluding a casino.

The ruling is a setback for efforts by the Tohono O'odham to build a $550 million complex, including a casino and hotel, on the edge of Glendale, near the Arizona Cardinals' stadium.

Gregory Mendoza, governor of the Gila River Indian Community, which opposes the O'odham plans, called Monday's ruling a "substantial victory." He said it provides another chance for opponents to persuade the Department of Interior to "consider the interests of all Arizona tribes this time."

But Tohono O'odham Chairman Ned Norris Jr. said he is "confident the nation will prevail" on other remaining questions about the tribe's right to build the casino, "just as we have on every single other issue that has been raised."