DENVER » The San Rafael Swell, with its miles of twisting sandstone spires and towering mesas, has long been a draw for hiking and canyoneering, and has even been considered for designation as a national monument.

So last month, when the federal Bureau of Land Management announced its intention to open portions of the 2,000-square-mile stretch of central Utah for drilling by private oil and gas companies, conservation groups reacted with alarm.

The debate over the proposed sale of drilling leases has rekindled tensions between those seeking to shield wilderness areas, and the Obama administration, which has come under pressure from oil and gas companies to develop more public lands as it pursues a policy of energy independence.

For nearly 100 years, the bureau has leased tracts of federally managed land to energy companies, which have sought to tap reserves in oil- and gas-rich states like Colorado, New Mexico and Utah. Disputes over the location of the drilling are not uncommon.

But the announcement that dozens of parcels would be auctioned off in the Swell, a largely untouched geologic formation, came as a surprise to environmental groups, who are worried that the administration’s energy strategy is shifting away from its promise to be environmentally sensitive.

"We were very surprised and disappointed to see this turn of events," said Steve Bloch, legal director for the Southern Utah Wilderness Alliance. "It’s a step backwards. To see a place like the San Rafael Swell be put up on the chopping block makes no sense."

On Monday, the Utah group, along with several other conservation organizations, filed a formal protest with the bureau, asking that it withdraw 55 of the proposed leases. The groups claimed the bureau had not sufficiently weighed the environmental consequences of opening parts of the Swell for drilling.

Bureau officials say that recent policy changes intended to slow the leasing process now ensure that tracts of land, like those within the Swell, are carefully examined before drilling is allowed. And they have disputed assertions that they are appeasing energy companies, which have been critical of the administration for being too restrictive.

"The B.L.M. is continuing to move towards full implementation of more environmentally responsible approaches to oil and gas development as outlined in our May 2010 leasing reforms," Celia Boddington, a bureau spokeswoman, wrote in an email. "Nationally, implementation is a work in progress but we are already seeing positive results."

According to bureau data, formal protests lodged over controversial leases were down, to 317 last year from 1,475 in 2009. Leases are also down. In the 2012 fiscal year, some 1,729 were issued, the fewest in any year for a decade, according to bureau data.

The leasing program has faced less opposition recently than it did during the Bush administration, when conservation organizations were mired in legal battles with the federal government over how tracts of land were sold.

Those disputes boiled over during the end of Bush’s presidency, when 77 oil and gas leases were sold near Utah’s national parks and recreation areas.

An environmental activist, Tim DeChristopher, went to prison for buying nearly $1.8 million worth of the leases without ever intending to pay.

In 2009, Interior Secretary Ken Salazar withdrew the leases, saying they had been rushed. A year later, the leasing program was revamped, seeking to better clarify which lands were appropriate for drilling.

Now, after energy companies nominate leases, state bureau offices must undertake a more stringent environmental review and leave more time for public comment before the auctions.

But environmental groups say those changes have been slow to take hold, and that parcels are being put up for lease in areas where they had fended off oil and gas drilling in the past.

In 2012 in Colorado, the bureau offered parcels near Mesa Verde National Park for lease, only to defer them before a February auction this year. A variety of organizations, including the state’s parks and wildlife agency and the National Park Service, raised concerns about the leases. Environmental groups said they expected the land to be proposed for leasing again.

In Utah, which has long been ground zero for the fight over public lands, environmentalists noted that the bureau itself considered some parts of the Swell to have wilderness characteristics.

The area does not, however, have federal protections that would bar drilling altogether. In 2002, Gov. Mike Leavitt suggested that the Bush administration designate a portion of the Swell as a national monument, but changed his mind after local residents opposed the idea.

And there are some who want to see development move forward.

"The environmental groups that are complaining don’t really know where the leases are or don’t care," said Commissioner Jeff Horrocks of Emery County, who said many in the mineral-rich area felt the Swell could be developed while also preserving the environment.

Cody Stewart, energy adviser to Gov. Gary R. Herbert of Utah, said that Herbert had no issue with the leases, and that there were other parts of the Swell that better warranted protection.

"We don’t see these leases as in high-priority conservation areas," he said.

Whether the land ultimately goes to auction, slated for November, is unclear.

Juan Palma, Utah director for the Bureau of Land Management, said the bureau was reviewing concerns about drilling in the Swell.

The bureau recently removed about 1,000 acres from the parcels set aside for auction — though the Utah wilderness group noted that that was only a small portion of the contested leases.

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