ST. GEORGE — County commissioners endorsed a proposed land deal that would nearly double the size of this fast-growing city by auctioning nearly 38 square miles of federal land to private developers.

Commissioners signed a resolution Tuesday, supporting the Washington County Growth and Conservation Act of 2006, a bill sponsored by Sen. Bob Bennett, R-Utah, and Rep. Jim Matheson, D-Utah.

"We consider it an extremely important piece of legislation ... for our future," said Jim Eardley, chairman of the Washington County Commission.

The bill offers wilderness protection for 343 square miles, although half of that already is protected inside Zion National Park and many other areas already are managed by federal agencies as potential wilderness.

The bill also would expand a preserve for the threatened desert tortoise.

Conservation groups have denounced the plan and vowed to hold it up in Congress, saying it ignores most lands worthy of wilderness protection in the county. The government owns 87 percent of Washington County land.

The commission's endorsement came after a consultant, Randy Johnson, said the land deals would start with 4,300 acres already identified by the U.S. Bureau of Land Management as suitable for sale.

Johnson said the bill authorizes — but doesn't require — the BLM to sell off 24,300 acres, The Spectrum of St. George reported.

But copy of the bill on Bennett's Web site says the Interior Secretary "must" sell the first 4,300 acres by 2013. It says the secretary could sell the other 20,000 unidentified acres starting in 2010.

The bill directs 85 percent of the money to the federal government for local conservation projects and a High Desert Off-Highway Vehicle Trail, according to Bennett's office.

The remaining 15 percent would go to the state, county and county water district.

The bill creates a corridor for a 120-mile water pipeline from Lake Powell as well as land for reservoirs, storage tanks, pump sites and flood-control projects.

Eardley said development fees, not money from land sales, would pay for the $370 million pipeline.