Senate Republicans have a message for President Obama as he prepares to deliver his State of the Union address on Tuesday: Approve the Keystone XL oil sands pipeline.

"Given the length of time your administration has studied the Keystone XL pipeline and the public’s overwhelming support for it, you should not further delay a decision to issue a presidential permit," all 45 GOP senators wrote Friday in a letter to Obama.

The controversial Canada-to-Texas pipeline, which needs a cross-border permit, has been in administrative limbo for five years. The State Department is finishing an environmental impact statement for the pipeline, which will be used to inform a decision on whether building the pipeline is in the national interest.

Republicans, centrist Democrats, unions and business groups say it is. They contend the pipeline will strengthen energy security by procuring crude from an ally, in turn displacing heavy crude imports from Venezuela, while bringing more than 42,100 direct and indirect jobs during a two-year construction phase, according to State Department estimates.

Keystone supporters also have held up the TransCanada Corp. project as a safer alternative to shipping crude by rail, which refiners have increasingly leaned on. Those arguments have been buoyed in recent weeks by a series of derailments of rail cars carrying crude.

"We need a safe and efficient system to transport crude oil in this country. The Keystone XL pipeline is a vital piece of the puzzle," the GOP senators said.

Obama, however, said in June that the pipeline's effect on greenhouse gas emissions is the metric by which he will approve or deny the project.

A draft environmental impact statement from the State Department said that Keystone wouldn't significantly exacerbate carbon emissions, as it suggested demand would get oil sands to market either by rail or other pipelines.

But environmental groups have challenged that assessment, saying Keystone would accelerate oil sands production, in turn facilitating greater consumption of the dense, carbon-intensive fuel. They also note the outside contractor who performed that study for State had previously done work for TransCanada. The State Department's Office of Inspector General is looking into a potential conflict of interest.

Green groups and liberal Democrats also have pushed back against Keystone boosters' claims about jobs, and even Obama himself has questioned its impact on employment. The State Department, for its part, has said Keystone's jobs effect would be "negligible," and predicts it would support 35 permanent jobs.

Opponents also have questioned if the oil sands Keystone would transport would stay in the U.S. once they reach Gulf Coast refineries or would be exported.