The Obama administration, under sharp pressure from officials in Nebraska and restive environmental activists, announced Thursday that it would review the route of the disputed Keystone XL oil pipeline, effectively delaying any decision about its fate until after the 2012 election.

The State Department said in a statement that it was ordering a review of alternate routes to avoid the environmentally sensitive Sand Hills region of Nebraska, which would have been put at risk by a rupture of the 1,700-mile pipeline carrying a heavy form of crude extracted from oil sands formations in Alberta to refineries in Oklahoma and the Gulf Coast.

The move is the latest in a series of administration decisions pushing back thorny environmental matters beyond next November’s presidential election to try to avoid the heat from opposing interests — business lobbies or environmental and health advocates — and to find a political middle ground.

President Obama delayed a review of the nation’s smog standard until 2013, pushed back offshore oil lease sales in the Arctic until at least 2015 and blocked new regulations for coal ash from power plants.

The proposed project by a Canadian pipeline company, TransCanada, similarly put the president in a political vise, squeezed between the demand for a secure source of oil and the thousands of jobs the project will bring, and the loud agitation of environmental advocates who threatened to withhold electoral support next year if he approved it.

Mr. Obama said in an interview with an Omaha television station last week that he would make the ultimate decision about the pipeline, but sought to portray Thursday’s announcement as solely a State Department matter and not the result of political calculation.

“I support the State Department’s announcement today regarding the need to seek additional information about the Keystone XL pipeline proposal,” the president said in a statement.

“Because this permit decision could affect the health and safety of the American people as well as the environment, and because a number of concerns have been raised through a public process, we should take the time to ensure that all questions are properly addressed and all the potential impacts are properly understood.”

He said he remained committed to a politically balanced diet of increased domestic oil and gas production combined with incentives for the development of carbon-free alternatives.

While environmental groups welcomed their temporary victory on the pipeline project, some expressed skepticism about the president’s motives. Glenn Hurowitz, an environmental activist and senior fellow at the Center for International Policy, said the delay could leave the final decision in the hands of Mr. Obama’s Republican successor.

“This decision just puts off a green light for the tar sands by a year,” Mr. Hurowitz said in an e-mailed statement. “That’s why I’m a little dismayed at suggestions that this kick-the-can decision means environmentalists will enthusiastically back President Obama in 2012. Is the price of an environmentalist’s vote a year’s delay on environmental catastrophe? Excuse me, no.”

Oil industry officials, some unions and the Canadian government said they were disappointed because the action delays what they call the economic benefits of the $7 billion project.

Jack N. Gerard, president of the American Petroleum Institute, said of the president’s decision, “This is all about politics and keeping a radical constituency, opposed to any and all oil and gas development, in the president’s camp in 2012. Whether it will help the president retain his job is unclear but it will cost thousands of shovel-ready opportunities for American workers.”

Andrew MacDougall, a spokesman for Stephen Harper, the Canadian prime minister, said, “While we are disappointed with the delay, we remain hopeful the project will be decided on its merits and eventually approved.”

TransCanada said that it would work with the State Department to find a new route, but warned that delay could kill the project, and with it tens of thousands of construction and related jobs and billions of dollars in tax revenues.

“If Keystone XL dies,” said Russell K. Girling, the company’s chief executive, “Americans will still wake up the next morning and continue to import 10 million barrels of oil from repressive nations without the benefit of thousands of jobs and long-term energy security.”

The Sand Hills region has a high concentration of wetlands, a sensitive ecosystem and extensive areas of very shallow groundwater that could be endangered by an oil spill. The State Department, which is responsible for approving transboundary pipelines, said that it expected that the review could be completed early in 2013.

Public officials and citizens in Nebraska have been vocal about the proposed pipeline route, not only because of fears about the Sand Hills region but because it will cross the Ogallala Aquifer, a critical source of drinking water for the Great Plains. Gov. Dave Heineman of Nebraska, a Republican, has been pushing for the pipeline to be rerouted and recently called a special legislative session to focus on Keystone XL.

“I am pleased that Nebraskans have been heard,” Mr. Heineman said in a telephone interview. “We’ve tried to make it very clear that we support the pipeline but oppose the route over the Ogallala Aquifer,” Mr. Heineman said, adding he was not expecting the State Department’s decision. “I hope we can find a common-sense solution, change the route and begin construction of the pipeline.”

The pipeline’s opponents in Nebraska hailed the decision as a pivotal victory, at least for now.

“This is a game changer for our state,” said Jane Kleeb, director of Bold Nebraska, a citizens’ advocacy group that has been leading efforts to block the pipeline. “We’ve been fighting this every day and night for almost two years.”

Kerri-Ann Jones in the State Department’s Bureau of Oceans and International Environmental and Scientific Affairs said the agency’s decision to look for alternative routes was sparked by the significant outcry from Nebraska residents and officials.

“What we’re hearing from the public and from comments across the nation is the concerns about it going through this fragile landscape,” she said of the proposed pipeline. “We’ve heard this loud and clear.”

Ms. Jones said that the previous environmental review of Keystone XL had not considered routes around the Sand Hills region in Nebraska, but rather routes that circumvented the state completely. New alternative routes for Keystone XL would still pass through Nebraska, but would seek to avoid or minimize any effect on the Sand Hills, she said.

The State Department’s inspector general announced on Monday that he was looking into charges of a conflict of interest and improper political influence in the preparation of the project’s environmental impact statement. Some have faulted the department for assigning the study to a company with financial ties to TransCanada.

Opponents of the project have organized two large protests outside the White House, including one on Sunday in which several thousand protesters encircled the mansion demanding that the president kill the pipeline. Earlier this year more than a thousand protesters were arrested in large demonstrations across from the White House.

(By John M. Broder and Dan Frosch*, The New York Times, 10/11/2011)

* John M. Broder reported from Washington and Dan Frosch from Denver; Ian Austen contributed reporting from Ottawa.