WASHINGTON - Pressure is mounting against a controversial bill that would designate wilderness and sell off about 25,000 acres of public land in southwestern Utah's Washington County.

Opponents fear Utah's Republican sponsor of the measure, Sen. Bob Bennett, will try to attach the bill to other legislation in the waning hours of the Republican-controlled Congress. Lawmakers have just days left in this Congress. Next year, Democrats take over both houses by a narrow margin.

Environmentalists and several members of Congress want Bennett to hold off this year.

The most recent opponents to weigh in were a handful of powerful senators, including Democrats Richard Durbin of Illinois, and Hillary Rodham Clinton of New York, and the chairman of the Shivwits Band of the Paiute Indian Tribe, located on the western side of Washington County.

The lawmakers and the band sent letters to key senators before a hearing last week asking them to block the bill.

Bennett and Utah Rep. Jim Matheson, a Democrat who sponsored a version in the House, say their bill would help balance conservation and rapid growth in the county. It would protect almost 220,000 acres as wilderness.

Critics say it would encourage development and threaten proposed wilderness in the region.

In a letter last week to key Senate leaders, the senators said the bill would harm public lands adjacent to Zion National Park and in the Mojave Desert recommended for wilderness designation under a rival bill, the America's Red Rock Wilderness Act.

"These public lands are an irreplaceable national asset," reads the letter signed by Durbin, Clinton and six others. The bill "falls well short of protecting this nationally recognized landscape by leaving out a vast majority of wilderness areas proposed by America's Red Rock Wilderness Act in that region of Utah."

The proposal would also threaten future wilderness by inviting new development in the rapidly growing county, the senators wrote.

Their letter is similar to one sent earlier by 47 House members.

Bennett has not made his plans clear, and his spokeswoman could not be reached immediately Wednesday afternoon. The hearing in the Senate last week was an important hurdle if Bennett wants to push the legislation through.

One potential way to block the measure could be through the Senate Indian Affairs Committee.

Glenn Rogers of the Shivwits Band wrote to the committee that the band was not adequately consulted about the bill and that as a result, it contains provisions that would harm the community. That includes trespassing and unmanaged off-road vehicle use on the reservation that could harm plants and animals, including the desert tortoise, which is important to the Shivwits. The tortoise is also listed as a threatened species under the Endangered Species Act.

"We request your assistance to ensure that the act is not hastily passed in the final days of this Congress," Rogers wrote.