The statements were contained a letter the county will send to the U.S. Department of the Interior and the Bureau of Indian Affairs.

The federal agencies are considering a Shingle Springs Band of Miwok Indians' request to take 5.6 acres into trust to facilitate construction of an interchange to enable motorists to reach the reservation -- and planned casino -- from Highway 50.

But county officials say an "environmental assessment" of the project under review by the BIA doesn't go far enough in identifying effects of the proposed casino resort. On Tuesday, the county requested that federal agencies demand a more extensive environmental study, saying documents submitted by the tribe fail to outline measures to minimize effects on traffic, air and water quality and nearby rural communities.

"The size, scope and nature of this project are unprecedented in El Dorado County and the surrounding region," the letter said.

For months now, representatives of the 300-member Shingle Springs tribe have been negotiating with the state Department of Transportation for an interchange the tribe would pay for.

Under their latest proposal, tribal chairman Nicholas H. Fonseca said, the Miwoks and their financial backers would spend $17 million for an overpass, a tunnel and interchange to the 160-

acre Shingle Springs Rancheria. The reservation land is north of the highway, between Shingle Springs and Greenstone roads.

The $125 million development includes a 250-room hotel, a convention center, a five-story parking structure and 3,000 parking spaces, according to documents the tribe prepared for the BIA. The 82,800-square-foot casino would house 2,000 slot machines.

Fonseca said the tribe plans to build the project in an aesthetically pleasing, environmentally sensitive manner.

"My own tribal members are very concerned with the same things that the people who are living in the surrounding communities and are driving up the freeway are concerned about," Fonseca said.

In its letter, the county says the tribe's documents "severely underestimate" the traffic the project would create on Highway 50.

Currently, about 45,500 vehicles a day pass along the stretch of highway near the planned casino. According to the tribe's studies, the project would generate an average of 8,326 trips on weekdays and 13,878 on Saturdays.

But county officials said traffic volume may be 1 1/2 times greater. They also say the project would result in double the air pollution estimated in the tribe's studies.

The county also expressed concern about the ability of a proposed wastewater treatment plant to handle the volume that will be created by the project.

Fonseca said his tribe is willing to work with the county on environmental issues and might be willing to pay for additional improvements to Highway 50.

County officials estimate that more than $3 million in road improvements would be needed to alleviate traffic from the project.

Fonseca warned officials not to try to stop the casino. "We're willing to negotiate with the county as long as they don't get ridiculous," he said in an interview.

Last year, supervisors approved a sweeping -- but unenforceable -- resolution opposing casino gambling in the county.

County counsel Tom Cumpston, who drafted the letter, warned supervisors about overplaying their hand.

"We can take the position that we're going to fight this project tooth and nail until the bitter end," Cumpston told the board. "And then we may find that this project goes in over our dead body without any mitigations."

Because the casino is proposed for reservation land, the tribe is not bound by the county's land-use rules.

Supervisor Rusty Dupray said the county may need to work with the tribe "if the ball is out of our court, and the Bureau of Indian Affairs and the federal government say they are entitled to do this."