WASHINGTON (AP) — The Senate killed Republican-backed attempts to overturn several of President Barack Obama's environmental and energy policies Thursday as lawmakers worked against a March 31 deadline to keep aid flowing to more than 100,000 transportation construction projects around the country.

The two-year, $109 billion transportation bill before the Senate has wide, bipartisan support, but has become a magnet for lawmakers' favorite causes and partisan gamesmanship. Among the amendments batted aside were GOP proposals to bypass Obama's concerns about the Keystone XL oil pipeline, to delay tougher air pollution standards for industrial boilers and to expand offshore oil drilling.

Action on those and other amendments came under an agreement between Senate Majority Leader Harry Reid, D-Nev., and Minority Leader Mitch McConnell, R-Ky., aimed at clearing the way for passage of the transportation bill next week.

Obama lobbied some Senate Democrats by telephone ahead of the Keystone vote, urging them to oppose an amendment by Sen. John Hoeven, R-N.D., that would have prevented the president from intervening in decisions related to construction of the pipeline and would have speeded its approval. Pointing to the administration's environmental concerns about the project, which would carry tar sands oil from Canada to the Texas Gulf Coast, Republicans accused Obama of standing in the way greater oil supplies at a time when Americans are coping with rising gasoline prices.

But some Democrats, especially those from oil producing states, were torn between support for the pipeline and their support for the president. The amendment was defeated 56-42, even though 11 Democrats broke ranks to support it. Sixty votes were needed for passage.

Republican leaders jumped on the White House lobbying.

"Most Americans strongly support building this pipeline and the jobs that would come with it," McConnell said in a statement.

The president's lobbying against the Keystone provision came "a week after the president signaled to me and to Sen. McConnell that he might be willing to work with us on some bipartisan steps forward on energy legislation that the American people support," House Speaker John Boehner, R-Ohio, told reporters. "If we're going to have bipartisan action on energy, the Keystone pipeline is an obvious place to start."

White House spokesman Jay Carney said Obama felt it was "wrong to play politics" with the pipeline, especially since the company behind the project has said it still was working on a final route that might satisfy environmental concerns. He also said it was "false advertising" to suggest the amendment would have any impact on gasoline prices.

Also defeated was an amendment by Sen. Susan Collins, R-Maine, which would have forced the Environmental Protection Agency to rewrite a rule requiring boiler operators to install modern emissions controls. Boilers are the second-largest source of toxic mercury emissions after coal-fired power plants. Collins said the EPA's rule would drive some manufacturers out of business.

And the Senate turned down an amendment to expand offshore oil drilling even though its sponsor, Sen. David Vitter, D-La., contended it would increase domestic energy supplies and reduce gas prices.

The transportation bill itself would overhaul federal transportation programs, including boosting aid to highway and transit programs, streamline some environmental regulations in order to speed up approval of projects and consolidate dozens of programs.

Lawmakers are under pressure to act quickly because the government's authority to collect about $110 million a day in federal gasoline and diesel taxes and to spend money out of the trust fund that pays for highway and transit programs expires at the end of the month. Chris Bertram, a Transportation Department official, said that if Congress doesn't meet the deadline, aid to about 130,000 transportation projects around the country will be disrupted and federal workers who send that money to states will be furloughed.

The construction industry, already suffering 17.7 percent unemployment at the end of January, would be especially hurt.

House Republicans crafted their own five-year, $260 billion bill, but they've been unable to marshal the support of rank-and-file lawmakers behind it. Conservatives say it spends too much money, while moderates say it would penalize union workers and undermine environmental provisions.

Boehner conceded Thursday that for the moment the House's best option is to take up the Senate bill after it passes — "or something like it" — although GOP leaders were still talking to their members in the hope of resurrecting their bill.

The inability of House Republicans to pass a highway bill of their own is an example of a paralysis that has struck several times in the past year. Last summer, an impasse over labor issues and subsidies for rural airports led to a two-week shutdown of non-essential Federal Aviation Administration operations.

In December, Boehner overrode his own rank-and-file when he agreed to a deal to extend the Social Security payroll tax cut after most lawmakers had gone home.