(Adds details, Senator Thune quote, background)
WASHINGTON, April 29 (Reuters) - U.S. Senate Majority Leader Harry Reid on Tuesday left open the possibility of voting on legislation forcing the approval of the long-delayed Keystone XL pipeline that would link Canada's oil sands to refineries in Texas.
"I'm open to anything that will move energy efficiency," Reid said in response to a reporter's question, referring to a bipartisan bill on promoting energy savings through revised building codes.
The Senate is expected to debate the efficiency bill this week. It is sponsored by Senators Jeanne Shaheen, a New Hampshire Democrat, and Rob Portman, an Ohio Republican.
The bill will likely be the last legislation debated on energy before midterm elections on Nov. 4, and Reid's comment suggested that a measure addressing Keystone approval could be added.
Reid said that talks with Republicans are continuing and initially he thought there would be a vote on a non-binding "sense of the Senate" resolution expressing support for TransCanada Corp's pipeline.
But now, Reid said, Republicans are asking for legislation that would have the force of law.
Earlier this month, the State Department said it would again delay a decision on the pipeline, approval of which has been pending for more than five years, until the Nebraska Supreme Court settles a dispute over what path the pipeline should take. The State Department leads the approval process because the pipeline would cross the national border.
The White House has threatened to veto previous attempts by Congress to force approval of the project, which would bring more than 800,000 barrels per day of Canada's oil sands petroleum to refiners along the U.S. Gulf.
The northern leg of the pipeline would link to a southern branch that is already operational.
The project divides Obama's base between environmentalists, who say the project would lead to an increase in emissions linked to climate change, and union members who say Keystone XL would create thousands of construction jobs.
Even if a measure attached to the Shaheen-Portman bill passed the Senate and a similar bill passed in the House of Representatives, it is unlikely the Senate would have enough votes to overcome any veto by President Barack Obama.
Senator John Thune, a South Dakota Republican, said Keystone supporters want more than a symbolic vote. "We ought to have a vote that matters," he said. "There should be a full blown debate on energy policy" in the Senate, he added. (Reporting By Richard Cowan, Timothy Gardner and Tom Ferraro; Editing by Ros Krasny and Sandra Maler)