Senate supporters of the long-delayed Keystone XL pipeline conceded Thursday they lack the 60 votes necessary to pass legislation authorizing immediate construction of the project, but said they remain hopeful of prevailing, according to the Associated Press.

In his latest effort to the long-delayed Keystone XL oil pipeline, Senator John Hoeven re-introduced legislation on Thursday that would force congressional approval of the controversial project, the AP reported.

"At this point we're still working to get 60," said Republican Senator John Hoeven from North Dakota, as he and Senator Mary Landrieu from Louisiana, introduced a bipartisan bill to end the delays and build the proposed oil pipeline from Canada to the United States, according to the AP. Hoeven is working with Senator Mary Landrieu, who heads the Energy Committee, to gather votes.

Hoeven said he has 55 co-sponsors for a bill that would take the power to approve the TransCanada Corp's pipeline out of the hands of the State Department and put it in the hands of Congress, the AP reported. The tally includes all 45 Republican senators plus 11 Democrats in the 100-member Senate, but is short of the 60 votes needed to clear procedural hurdles.

The Keystone XL pipeline divides President Barack Obama's base between environmentalists, who say it would boost emissions linked to climate change, and union supporters who say it would create thousands of construction jobs, according to the AP. It was unclear if the bill would even get a vote in the Senate, which is controlled by Democrats, or if any more Democrats could be persuaded to support it.

"I don't know if we will get 60," Hoeven said, the AP reported. "At this point I have a lot of maybes, but I don't know how many will end up voting with us."

Senate Majority Leader Harry Reid said he was considering allowing a vote on Keystone in some form on Tuesday but only if it could also help push through a bipartisan bill on energy efficiency, according to the AP. Senior Democratic aides said on Thursday a decision on how to proceed would likely be made early next week.

Hoeven said the wider energy bill, which focuses on increasing energy efficiency through tighter building codes, could get held up if there is no Keystone vote, the AP reported.

"To move forward on energy efficiency, we are going to have to get a vote on Keystone," Hoeven told reporters, according to the AP.

The Obama administration has been considering Keystone for over five year, which would bring 800,000 barrels per day of mostly Canadian oil sands petroleum to Texas refineries, the AP reported.

The State Department said earlier this month it would delay deciding whether the pipeline is in national interest until a legal dispute is settled in Nebraska, according to the AP.