WASHINGTON — Congress never intended for Indians to build Nevada-style casinos away from their reservations, and tribes risk a backlash by pursuing the trend, Sen. John McCain said Tuesday.

"None of us ever anticipated that there would be casinos in the Catskills," McCain, chairman of the Senate Indian Affairs Committee, told a tribal leader from New York who's pursuing such a project.

"We're seeing casinos in downtown Oakland and downtown Denver. . . . If we have enough off-reservation casinos set up in America we're going to see a backlash against Indian gaming, because that was not the intent of the law," said McCain, R-Ariz.

The projects near Oakland and on the outskirts of Denver have not been approved, but several tribes have succeeded in establishing off-reservation casinos, and many more are pursuing them.

The trend has surfaced as Indian gambling has transformed in recent years from a relatively small industry into a huge one, generating an estimated $18.5 billion in 2004, nearly double the take from Nevada's gambling industry.

Not all tribes have benefited. Those with reservations near populated areas have been able to cash in, while those with remote reservations have often struggled. Some of those have sought to lay claim to better-situated land and build casinos there.

Under the 1988 Indian Gaming Regulatory Act, off-reservation gambling is allowed only under a narrow set of exceptions, but tribes are increasingly pursuing those options or finding other ways. In the Oakland case, a tribe got a friendly lawmaker to insert language into a federal spending bill designating special federal trust land.

McCain said after the hearing that he was still deciding whether to introduce legislation to further restrict off-reservation gambling. "I think that there is a problem," he said.

In the House, Resources Committee Chairman Richard Pombo, R-Calif., has circulated draft legislation that would restrict off-reservation casinos to "Indian Economic Opportunity Zones" where numerous tribes could build casinos in one area.

McCain heard different perspectives from tribal leaders at Tuesday's hearing.

James W. Ransom, chief of New York's St. Regis Mohawk Tribe, which is trying for a Catskills casino, said tribes should be allowed to build off-reservation.

"What if it's in a tribe's and a state's mutual interest to pursue off-reservation gaming?" he asked.

But Deron Marquez, chairman of the San Manuel Band of Mission Indians, which operates a profitable casino in Southern California, said he opposed the trend. Marquez's tribe faces potential competition from several other tribes that want to locate nearby.

"If these are allowed to go through, as I said in my testimony, this will be the end of what we know as tribal government gaming," Marquez said.

Tribal leaders also came under fire at the hearing for refusing to reveal their revenues. There is no requirement for tribes to open their books to the non-tribal public, and most of them don't.

"Every other form of government in this country, county, state, municipal and federal government publishes their numbers," Sen. Tom Coburn, R-Okla., told tribal leaders. "Transparency and sunshine is great for you in the long run."