The Republican-led U.S. House of Representatives approved the Keystone XL pipeline on Friday, but a similar measure struggled to get enough support in the Senate and President Barack Obama indicated he might use his veto if the bill does get through Congress.

The legislation, approved by 252 votes to 161, circumvents the need for approval of TransCanada Corp's (TRP.TO) $8 billion project by the Obama administration, which has been considering it for more than six years. No Republicans voted against the measure, while 31 Democrats voted for the bill.

It was the ninth time the House has passed a Keystone bill, and supporters were confident that this time the Senate would follow suit and pass its version.

But passage was not assured in the Senate, which is expected to take up the measure next Tuesday. Supporters were still one vote shy of the 60 needed to overcome a filibuster, a blocking procedure, an aide to a Keystone supporter said on Friday. The aide spoke on condition of anonymity.

Approval for the pipeline, which would help transport oil from Canada's oil sands to the U.S. Gulf coast energy hub, has rested with the Obama administration because it crosses an international border.

The decision has been pending amid jousting between proponents of the pipeline who say it would create thousands of construction jobs and environmentalists who say it would increase carbon emissions linked to climate change.

If the measure did pass Congress Obama would have to decide whether to make rare use of his veto power.

While the White House has not said if he would do this, Obama has threatened to use his veto in the past. On Friday, he said he still favored the evaluation that is being carried out by the State Department.

Noting legal action in Nebraska, where a court is expected to rule in coming weeks on a case over the pipeline's route in the state, Obama said "until we know what the route is it's very hard to finish that evaluation. And I don't think we should short-circuit that process."

The House vote would have no effect on the State Department's review, department spokeswoman Jen Psaki told a briefing. She did not say when it would be completed.

LOUISIANA PUSH

The push on the Keystone XL pipeline this week followed heavy defeats for Obama's Democratic Party in midterm elections on Nov. 4 and was propelled by a runoff election battle for a Senate seat in Louisiana, whose economy is heavily oil-dependent and where both candidates are keen to show support for the pipeline.

Democratic Senator Mary Landrieu, the head of her chamber's energy committee, is co-sponsoring the Keystone bill in the Senate with Republican John Hoeven of North Dakota.

The bill's sponsor in the House was Republican Representative Bill Cassidy from Louisiana, who is seeking to unseat Landrieu in their runoff on Dec. 6.

Since all 45 Senate Republicans support the bill, backers of the bill need 15 Democrats. But several Democrats who backers were trying to win, including Chris Coons of Delaware, and Ben Nelson of Florida, said this week they will vote against the bill on Tuesday.

Still, the prospects for Keystone approval by Congress will likely improve in January when the Senate switches to Republican control after this month's elections.

If the bill does not pass on Tuesday, Hoeven plans to reintroduce it next year. "I believe I have the votes to pass it then," he said.

Obama, who spoke at a news conference in Myanmar, said he has had to constantly push back against the idea that Keystone is a "massive jobs bill."

Introducing a fresh debating point, Obama also rejected the idea it would lower gas prices in the U.S., saying it would provide Canada the ability to pump its oil, and "send it through our land, down to the Gulf, where it will be sold everywhere else. That doesn't have an impact on U.S. gas prices"

Shares in TransCanada were down 36 Canadian cents to C$56.09 on the Toronto Stock Exchange.