BUFFALO - A federal judge ruled Tuesday that gambling is not legal on a nine-acre site where the Seneca Indian Nation has begun building a $333 million casino complex, leaving the future of one of the most expensive private projects ever planned for Buffalo in doubt.

In a 127-page ruling, U.S. District Judge William Skretny vacated a decision by the National Indian Gaming Commission to allow gambling on the off-reservation site, which the western New York tribe purchased in 2005.

The judge said that while the land qualifies as “Indian lands” within the meaning of the federal Indian Gaming Regulatory Act, it is not eligible for gaming because it was not acquired as part of a land claim.

The Senecas have been operating a small temporary casino on the site while building the permanent one.

It was not clear Tuesday whether that will remain open.

Seneca President Maurice John said the tribe planned to discuss its options with federal officials who have jurisdiction over Indian gaming.

“The court's decision is lengthy and requires much closer analysis,” John said in a statement. “We will be reviewing the decision carefully, as we want to be sure that the court was aware of and considered all of the applicable federal law.”

Casino opponents who brought the lawsuit against the National Indian Gaming Commission and Department of the Interior said the temporary casino should close, even if Skretny's decision is appealed.

“The court has voided and vacated their approval of gambling,” said Richard Lippes, attorney for Citizens for a Better Buffalo. “That being the case, if they continue to gamble they will be doing so illegally and doing so in violation of the New York State Constitution.”

In his decision, Skretny said that the National Indian Gaming Commission's 2007 determination that the Buffalo parcel is eligible for gaming was “arbitrary, capricious and not in accordance with the law.”

The IGRA prohibits gambling on land acquired after 1988 except in certain cases, including when the land was part of the settlement of a land claim. The NIGC had said that the Buffalo land met that exception because the Senecas acquired it with funds from the Seneca Nation Settlement Act of 1990.

That act renegotiated an unfair lease agreement with the Senecas for land occupied by the city of Salamanca.

Skretny ruled that the Salamanca lease situation was not a land claim and that “because no claim existed, no claim was settled.”

In addition to the small temporary casino, the Senecas operate two successful casinos in Niagara Falls and on reservation land in Cattaraugus County.

The Buffalo casino would be the third and final one allowed under a 2002 agreement with the state that requires the tribe to share a percentage of slot machine revenues with the state and host communities.

The Senecas initially planned a $125 million casino in Buffalo but last year expanded plans to include a 22-story luxury hotel, three-acre public park and an artificial creek.

Tuesday's ruling does not prevent the Senecas from developing the site with something other than a casino.

Opponents say they worry a casino would drain money from the already struggling Buffalo economy, cause a net loss in jobs and a host of social ills.

The Seneca Nation last month said its gaming operations employ more than 5,000 people in western New York.