(Recasts with vote-seeking at Democratic luncheon)
By Timothy Gardner and Susan Cornwell
WASHINGTON, Nov 18 (Reuters) - Keystone XL's top supporter in the U.S. Senate frantically lobbied colleagues on Tuesday in a last-ditch attempt to find enough "yes" votes to approve the oil pipeline from Canada.
With the 100-member chamber one vote short of the needed 60 to pass a version of a bill that sailed through the House of Representatives last week, Senator Mary Landrieu of Louisiana, who co-sponsored the bill, urged fellow Democrats to support it during a long luncheon in the Capitol.
"It was painful. Landrieu was kind of begging for votes, and some Democrats would say 'no' and then argue with her and with each other," said a Senate Democratic aide who did not want to be identified.
The aide said that Landrieu had been "calling senators all week, texting them every other hour" to try to get votes.
The Senate is expected to vote as early as 5:30 p.m. EST (2230 GMT) on Tuesday.
TransCanada Corp's Keystone XL pipeline has broad support in Louisiana, an oil-producing state, where Landrieu faces an uphill battle to win a new six-year term in a December run-off election.
Republican Senate staffers pressured Democrats including Chris Coons of Delaware and Dick Durbin of Illinois, to reverse their opposition to the $8 billion pipeline, with little luck. "He's still a no," a Coons aide said Tuesday.
Durbin, from an industrial state dependent on energy, was seen as a long shot as possible yes vote, even though he has voted against the pipeline several times. Durbin has not indicated how he would vote this time, his spokesman said.
Senator Angus King, an independent from Maine, had been thought a possible 60th "yes" but said on Tuesday he would vote no. "Congress is not - nor should it be - in the business of legislating the approval or disapproval of a construction project," King said in a news release.
Republican Senator John Hoeven of North Dakota, who introduced the bill with Landrieu, was asked by reporters at the Capitol if there were enough votes. "I think so," he said.
Construction workers, unions and energy companies say the pipeline, which would transport more than 800,000 barrels of oil a day from Alberta to Nebraska en route to the Gulf of Mexico, would create thousands of jobs.
But many environmentalists oppose the project, saying the oil sands would spike carbon emissions linked to climate change and that the oil could be sold abroad.
TransCanada, which has already built a pipeline to the Gulf Coast that would connect with Keystone XL, says the new link would take two years to complete once approved. As oil prices have fallen more than 25 percent since the summer, Keystone XL could be an increasingly important piece of the puzzle for the development of Canada's oil sands.
Activists with the environmentalist group 350.org on Tuesday protested at the offices of Democratic Senators Tom Carper of Delaware and Michael Bennet of Colorado, who said recently they will support the bill.
"If we allow this pipeline to go through, we are moving backwards on clean energy," said Nebraska Art Tanderup at a planning meeting for the protest, adding that his Nebraska farm sits in the middle of the proposed pipeline route.
If Keystone does not pass, Hoeven plans to reintroduce the bill in January or February, when it has a better chance of obtaining 60 votes after Republicans picked up seats in the midterm elections. Next year Hoeven could also attach a Keystone measure to a wider bill that Obama would find hard to veto.
Obama has not indicated whether he would veto. But he raised new questions about the project during a trip to Asia late last week, saying Keystone would not lower gas prices for U.S. drivers but would allow Canada to "pump their oil, send it through our land, down to the Gulf, where it will be sold everywhere else."
Republicans and energy analysts said those comments likely mean Obama is leaning toward veto.
King, who often votes with Democrats, had been seen as a possible swing vote despite his support of climate activism. He said he was "frustrated" by President Barack Obama's failure to make a decision on the pipeline that has been pending for six years and urged him to make a decision soon.
TransCanada shares closed down 57 Canadian cents at C$56 on the Toronto Stock Exchange on Tuesday. (Additional reporting by Susan Heavey, Valerie Volcovici, Ros Krasny, Amanda Becker, and Richard Cowan; editing by Steve Orlofsky, Bill Trott, Paul Simao, Matthew Lewis and Cynthia Osterman)