Federal land managers will issue a long-awaited report Tuesday detailing how much of the country's onshore oil and gas are available for drilling -- data that could shape the debate over land-use restrictions on energy companies seeking access to prized reserves.

The report comes three years after a study commissioned by a 2000 energy bill found that more than 80 percent of the reserves is already available for development.

That assessment was popular with environmentalists, who use it to argue that the industry does not need special breaks to get access oil and gas under federal lands, some of it locked beneath pristine Rocky Mountain wild lands.

But energy companies said the earlier study didn't tell the full story, and they lobbied for an updated tally, which was mandated by the Energy Policy Act of 2005.

Environmentalists and industry advocates expect the new inventory to show that energy companies face more restrictions than the Bureau of Land Management previously reported.

The updated study examines a wider geographic area, including regions east of the Mississippi River and a northern Alaska basin that includes the Arctic National Wildlife Refuge, said Matt Spangler, a BLM spokesman. Lawmakers have battled for 25 years over whether to tap vast oil reserves on the 19-million-acre Alaska refuge.

The new study also considers the effect of conditions placed on drilling permits, such as restrictions on wintertime drilling to protect elk and deer.

Industry lobbyists have long argued they face troublesome bureaucratic hurdles to get access to domestic oil and gas resources. The new report could give them added ammunition when talking to lawmakers and agency officials about streamlining the permitting process.

"It will absolutely help in giving policy makers a better understanding of what (drillers) are facing," said Dan Naatz, an Independent Petroleum Association of America vice president.

But environmentalists, who have worked to stave off drilling in areas proposed for protection, fear the report will be slanted toward industry.

"I hope we won't have an example of the Bush administration interfering with science for political reasons, but I'm afraid that's what we're going to be seeing here," said Dave Alberswerth of the Wilderness Society.

BLM Director Kathleen Clarke will unveil the new inventory today.

The 2003 study focused on resources in Western states from New Mexico to Montana, including the Greater Green River and Powder River basins. The new inventory analyzes the extent to which oil and gas beneath 99 million acres of federal lands are available for leasing. It includes land in Florida, the deep South and the Appalachian Mountains.

This story appeared in The Daily Herald on page D6.