WASHINGTON (AP) — The White House on Tuesday threatened to veto the first piece of legislation introduced in the Republican-controlled Senate, a bill approving the much-delayed Keystone XL oil pipeline, in what was expected to the first in many confrontations over energy and environmental policy.

Hours after supporters of the bipartisan bill, sponsored by all 54 Republicans and six Democrats, announced its introduction, the White House said for the first time that President Barack Obama would veto it.

White House press secretary Josh Earnest said Tuesday he does not expect Obama would sign any Keystone legislation that reaches his desk. He said legislation should not undermine a "well-established" review process being run by the State Department or circumvent a lawsuit still pending in Nebraska over the pipeline's route.

The two main sponsors, Sen. Joe Manchin, D-W.Va., and Sen. John Hoeven, R-N.D., said Tuesday morning they had enough votes to overcome a filibuster of the bill but not a presidential veto. The House is expected to vote and pass a bill approving the $5.4 billion project, which was first proposed in 2008, on Friday.

"The Congress on a bipartisan basis is saying we are approving this project," said Hoeven, the chief Republican sponsor. He said if the president chooses to veto the bill, he would work to attach it to a broader energy package or must-pass spending bills.

The bill is identical to one that failed to pass the Senate by a single vote in November, when Democrats were in control and Sen. Mary Landrieu of Louisiana pushed for a vote to save her Senate seat. She lost to Republican Rep. Bill Cassidy, who sponsored the successful House bill approving the pipeline.

But now the odds of passage are much improved with the Republican takeover of the Senate. The bill will also test Republicans' commitment to more open debate. Hoeven and Manchin said they welcomed additions to the bill, which they hoped would increase support.

In a letter to Democrats from their leadership obtained by the AP, Sen. Chuck Schumer of New York and Sen. Debbie Stabenow of Michigan said the Keystone bill was "the first opportunity to demonstrate that we will be united, energetic, and effective in offering amendments that create a clear contrast with the Republican majority."

Among the ideas suggested in the letter were measures to prohibit exporting the oil abroad, to ensure American iron, steel and other goods were used in the pipeline's construction and to match every job created by the pipeline with an investment in clean energy.

In recent months, Obama has been increasingly critical of the project, and has resisted prior efforts to fast-track the process. At his year-end news conference, Obama said the pipeline would benefit Canadian oil companies but would not be a huge benefit to American consumers, who are already seeing low prices at the pump thanks to oil prices, which on Monday dipped to a nearly six-year low and were sharply down again Tuesday.

In addition, the outcome of a Nebraska lawsuit over the route of the pipeline is still pending. Another challenge to the pipeline is being waged by a South Dakota tribe over renewal of an application for a permit.

The project by Calgary-based TransCanada would move tar sands oil from Canada 1,179 miles south to Gulf Coast refineries. Supporters say it would create jobs and ease American dependence on Middle East oil. A government environmental impact statement also predicted that a pipeline would result in less damage to the climate than moving the same oil by rail.

Critics argue that the drilling itself is environmentally harmful, and said much of the Canadian crude would be exported with little or no impact on America's drive to reduce oil imports, which have already been greatly reduced because of record U.S. oil production.