DENVER — Environmental groups are threatening to sue the federal government to block plans for commercial oil-shale development on nearly 2 million acres of public land in Colorado, Utah and Wyoming.

Twelve groups sent letters tto the Interior Department and Bureau of Land Management last week saying they will sue unless the potential impacts on endangered species are addressed.

They argue the final plan and rules approved late last year violated federal law because the agencies didn't formally consult with the U.S. Fish and Wildlife Service.

"They cut Fish and Wildlife Service out of it," said Melissa Thrailkill, an attorney with Center for Biological Diversity in San Francisco.

Documents obtained by the groups under the Freedom of Information Act show that Fish and Wildlife Service biologists were concerned about "information gaps" in the BLM's environmental analysis. The biologists suggested barring leases in habitat for threatened or sensitive species, the documents show.

"In its rush to pave the way for oil-shale development before leaving the office, the Bush administration broke the law once again by refusing to protect the West's endangered wildlife," Thrailkill said.

BLM spokesman Matt Spangler said the agency had no comment on the environmental groups' claims.

Colorado Gov. Bill Ritter and other state officials have urged federal officials to delay a final plan and rules for commercial oil-shale development, saying there are too many unanswered questions about the effects on water, wildlife, air and local economies.

They point out that companies are still experimenting with the technology and that industry and government officials acknowledge that commercial development is several years away.

In November, Wyoming Gov. Dave Freudenthal asked the BLM to remove the Adobe Town badlands in southwest Wyoming from land available for lease.

The Bush administration released the final plan for opening the land to shale development in November, a few weeks after a congressional ban on using federal funds to write final regulations expired.

One of the ban's sponsors was Sen. Ken Salazar, D-Colo., nominated by President-elect Barack Obama to head the Interior Department.

Shale deposits in northwest Colorado, Wyoming and Utah are thought to hold more than 1 trillion barrels of oil. About 800 billion barrels of that are believed to be recoverable.

Four companies have received 160-acre parcels of public land for oil-shale demonstration projects in Colorado and Utah, and Shell Exploration & Production has been running tests on private land in Western Colorado since the mid-1990s.