Key US senators unveiled largely symbolic legislation on Wednesday aiming to require President Barack Obama to allow the controversial US-Canada "Keystone XL" pipeline project to move ahead.

"It would create jobs almost immediately -- a lot of jobs," said Republican Senate Minority Leader Mitch McConnell, one of the bill's top backers, who accused Obama of trying to "curry favor" with environmentalists by delaying the project.

The measure aims to require US Secretary of State Hillary Clinton to issue a permit within 60 days to allow the project to move forward unless Obama formally declares it not in the national interest.

The proposal, which Obama's Democratic allies can block, also requires that the permit "contain strong and specific environmental protections and protect states' rights," according to a summary of the legislation.

The measure declares that the project, which has drawn fierce opposition from environmentalists, would promote job creation and economic growth at a time when US voters worry about unemployment ahead of November 2012 elections.

Republican Senator Dick Lugar, the bill's chief author, called the pipeline "a dramatic opportunity to create jobs now" and said the project could ultimately lead to the employment of 20,000 people.

The Obama administration earlier this month said it would study an alternate route for the oil pipeline, and pushed back its final decision on the project until 2013 -- after next year's presidential elections.

The new bill requires the permit to recognize an alternative route recently approved by Nebraska to ensure that the pipeline steers clear of the northern US state's sensitive wetlands.

Pipeline operator TransCanada Corp has agreed to reroute the Keystone XL pipeline project after Nebraska lawmakers introduced the legislation in a special session.

Environmental activists fear an accident along the 1,700-mile (2,700-kilometer) pipeline would be disastrous for aquifers in central US Great Plains states.

Others oppose the $13 billion project because exploiting the tar sands requires energy that generates a large volume of greenhouse gases that scientists blame for global warming.

At the US State Department, spokesman Mark Toner said officials there would "work closely and consult closely with Congress" as the review process unfolds but declined to comment directly on the legislation.