By Ros Krasny

WASHINGTON, Feb 12 (Reuters) - A Republican lawmaker has urged U.S. authorities not rush to settle with BP Plc under the U.S. Clean Water Act in a court case starting this month related to the 2010 Deepwater Horizon oil spill.

David Vitter, the top Republican on the Senate Committee on Environment and Public Works, said in a letter to Attorney General Eric Holder on Tuesday that he was concerned BP "may take advantage of the overlap" between two laws "to continue intentionally slow-walking restoration efforts" under a related Natural Resources Damage Assessment, or NRDA.

After the April 2010 explosion on the Transocean rig in the Gulf of Mexico, 4.9 million barrels of oil spewed into the Gulf over 87 days. Shorelines from Texas to Florida were fouled before responders could cap the mile-deep (1.6 km) well.

BP could face massive civil penalties of up to $21 billion if found to be grossly negligent for the worst offshore oil spill in U.S. history. The Justice Department will make its case at a trial starting in New Orleans on Feb. 25.

The company already agreed in January to pay a record $4 billion in criminal penalties for the Deepwater Horizon disaster, related to workers' deaths and other charges.

Even though the potential payout under the Clean Water Act is massive, if BP is allowed to settle before agreement is reached on separate penalties expected under the NRDA, states might rush to pay for clean-up projects using the CWA dollars, Vitter, from Louisiana, said in the letter.

Those funds "may be misdirected to restoration projects that should be covered by NRDA dollars," he said.

"I ask that the Department of Justice not settle with BP for fines due under the Clean Water Act until agreement on the responsibility for Natural Resources Damage Assessment has been reached," Vitter said.

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