The federal government is urging a Sonoma County Indian tribe to consider alternatives to creating a new reservation south of Petaluma, citing expected new rules that could limit what critics call ?reservation shopping.?

Citing ?the changing gaming environment? and ?concerns advanced by local jurisdictions,? a letter from an Interior department official to the Dry Creek Rancheria says the government may tighten the rules governing how land is taken into trust for tribal reservations.

That, in turn, could limit the building of new casinos to existing reservations.

Though the tribe says it is not planning to build a casino on the 277 acres of land it owns south of Petaluma, east of Highway 101 near Kastania Road, local officials have been skeptical of those claims and have moved to rally opposition to any gaming there.

A November advisory vote in Petaluma, asking voters to authorize the City Council to ?take all lawful steps? to oppose a casino on the site, received 80 percent approval, and such community input will be taken into account when weighing new trust applications, the government?s letter indicates.

James Cason, associate deputy secretary for the Interior department, wrote in the Feb. 13 letter that ?we also plan more detailed consideration of the broad implications associated with new gaming operations with established communities where gaming is not currently conducted.?

The 931-member Dry Creek tribe, which operates River Rock Casino in Geyserville, applied last year to have the Petaluma site taken into trust, saying in its federal application that it ?intends to develop? a casino there.

However, a tribal spokesman has said the application is routine paperwork as part of the federal trust process and denied any plans for a casino. The tribe has repeatedly said it is only using the site for agricultural operations.

Earlier this year, Tribal Chairman Harvey Hopkins met with Sonoma County Supervisor Mike Kerns, Petaluma Mayor Pamela Torliatt and other officials to talk about future development of the site.

Officials who attended the meeting said the tribe had no specific plans for the property and indicated that it wants whatever might be built there to have the support of the community.

Cason?s letter, similar versions of which were sent to 35 other tribes, says changes to the regulations governing the trust process ?may result in fewer off-reservation properties taken into trust.?

He writes, ?In particular, we expect to consider a paradigm where the likelihood of accepting off-reservation land into trust decreases with the distance the subject parcel is from the tribe?s established reservation or ancestral lands, and the majority of tribal members.?

The issue of whether the Petaluma site is ancestral land for the Pomo tribe is disputed. The Graton Rancheria of Coast Miwok Indians, which is planning its own casino in Rohnert Park, says Petaluma is Miwok territory, but the Pomo tribe says its ancestors lived in modern-day south Sonoma County as well.

The letter urges the tribe to become ?fully aware of the changing environment and to discuss the risks of pursuing an off-reservation gaming application.?

In addition, the relative risks, costs and benefits of ?an alternative on-reservation gaming initiative? should be considered by the tribe, the letter states.

The tightening of federal regulations referred to in the letter follows Gov. Arnold Schwarzenegger?s policy not to approve any new gaming compacts unless several criteria are met, including the support of the ?affected local community? demonstrated by an advisory vote or other means.