Ms. Jackson had made clear her intention to follow her scientific advisers and set a new standard within the more restrictive range by the end of this year. She has told associates that her success in addressing this problem would be a reflection of her ability to perform her job. The agency sent the now-rejected standards to the White House in July with the expectation that they would be issued by Aug. 31.

While some senior agency officials expressed disappointment with the decision, they also said they understood that it was their job to offer their best technical advice to the White House and that the ultimate decision rested with the president, who has to stand for re-election and consider other factors.

Reaction from environmental advocates ranged from disappointment to fury, with several noting that in just the past month the administration had tentatively approved drilling in the Arctic, given an environmental green light to the 1,700-mile Keystone XL oil pipeline from Alberta, Canada, to Texas and opened 20 million more acres of the Gulf of Mexico to drilling.

Daniel J. Weiss, senior fellow at the Center for American Progress, said, “Today’s announcement from the White House that they will retreat from implementing the much-needed — and long-overdue — ozone pollution standard is deeply disappointing and grants an item on Big Oil’s wish list at the expense of the health of children, seniors and the infirm.” The center is a liberal research group with close ties to the White House.

Bill McKibben, an activist leading a two-week White House protest against the pipeline project which has resulted in more than 1,000 arrests, said that the latest move was “flabbergasting.”

“Somehow we need to get back the president we thought we elected in 2008,” he said.

Cass R. Sunstein, who leads the White House office that reviews all major regulations, said he was carefully scrutinizing proposed rules across the government to ensure that they are cost efficient and based on the best current science. He said in a letter to Ms. Jackson that the studies on which the E.P.A.’s proposed rule is based were completed in 2006 and that new assessments were already under way.

The issue had become a flashpoint between the administration and Republicans in Congress, who held up the proposed ozone rule as a test of the White House’s commitment to regulatory reform and job creation. Imposing the new rule before the 2012 election would have created political problems for the administration and for Democrats nationwide seeking election in a brittle economy.