Five of Nebraska’s 49 state senators have jumped into the debate over how quickly federal officials should decide whether to approve a pipeline that would carry Canadian tar sands oil to refineries near the Gulf of Mexico.

The state senators wrote a letter requesting the decision be delayed until next May, so Nebraska would have another chance to pass oil pipeline regulations.

The U.S. State Department has said it would decide the project’s fate by the end of 2011. Some Congressional Republicans want a Nov. 1 deadline.

TransCanada’s proposed Keystone XL project is designed to carry oil from Canada across Montana, South Dakota, Nebraska, Kansas, Oklahoma and Texas. TransCanada also has proposed connecting it to the Bakken oil field in Montana and North Dakota.

Nebraska lawmakers gave final approval Thursday to a law that would hold companies responsible for restoring areas where oil pipelines are installed and operated. But lawmakers were unable to agree on rules governing pipeline locations, state permitting or liability standards.

“We ask that the State Department delay the permit of the proposed Keystone XL pipeline to give the legislature more time to both study and enact necessary legislation in the 2012 legislative session,” state Sen. Ken Haar of Malcolm said.

The other state senators who signed onto the letter are Colby Coash of Lincoln, Annette Dubas of Fullerton, Tony Fulton of Lincoln and Kate Sullivan of Cedar Rapids.

Calgary-based TransCanada submitted its Keystone XL project for State Department review in late 2008. The State Department has authority over the pipeline because it crosses an international boundary.

The State Department said last month that a new environmental study on the pipeline revealed no new issues since a similar report was issued last year.

But environmental groups have raised concerns that the pipeline could foul underground and surface water supplies, increase air pollution around refineries and harm wildlife. They also have speculated about what they consider inadequate pipeline safety and emergency spill responses.

The pipeline’s proposed route crosses the massive underground Ogallala Aquifer, which supplies water for irrigation and drinking to people in eight U.S. states.

Supporters say the project could be a boon for U.S. jobs and energy production while strengthening a friendly source of oil. TransCanada has promised that the pipeline would be safe and reliable.

The Keystone XL project is the second phase of a massive underground pipeline network designed to move 1.5 million barrels of Canadian oil daily to U.S. refineries. TransCanada’s initial Keystone pipeline began carrying crude oil across Saskatchewan and Manitoba and through North Dakota, South Dakota, Nebraska, Kansas, Missouri and Illinois last June.