* Final accord would settle environmental groups' lawsuit
* Wildlife observers to be placed on burn vessels
* Weather to prevent further burnings before Tuesday (Updates with interim deal reached; court hearing postponed; adds byline)
By Mary Rickard
NEW ORLEANS, July 2 (Reuters) - Environmental groups, BP (BP.N) (BP.L) and the U.S. Coast Guard reached tentative agreement on Friday on measures to prevent sea turtles from being incinerated alive in controlled burns of spilled oil in the Gulf of Mexico.
The deal would settle a lawsuit accusing BP of violating the U.S. Endangered Species Act and terms of its lease with the federal government for the deep-sea well that ruptured on April 20, unleashing the worst offshore spill in U.S. history.
Among the creatures most at risk from the incineration of oil at sea are the endangered Kemp's ridley turtle, the smallest known sea turtles in the world and among the rarest.
The four conservation groups bringing the suit amended the complaint on Thursday to add the Coast Guard as a defendant.
Under the accord reached in talks on Thursday evening and Friday morning, the parties agreed to a plan allowing biologists or other trained wildlife observers to accompany oil-incineration vessels at sea to remove as many turtles as possible from designated areas before burning starts.
Private boat captains chartered for wildlife rescue missions in the Gulf said in affidavits filed with the lawsuit that young sea turtles tend to congregate among oil blobs floating in the water, apparently unable to distinguish between the oil and mats of seaweed that provide natural shelter on the surface of the Gulf.
The turtles are then presumably swept up and unable to escape when shrimp boats contracted for cleanup operations are used to drag fire-resistant booms to encircle the floating oil before it is set ablaze.
The interim agreement was presented in federal court in New Orleans on Friday to U.S. District Judge Carl Barbier, who is presiding over the case, and the plaintiffs suspended their request for an immediate court order to bar future oil burns.
"The parties have agreed between now and next week on implementing an additional measures to ensure any endangered species are protected," Barbier said. "We are not going to litigate today."
Precise details of the plan for safeguarding turtles will be worked out on an "expedited basis" between the Coast Guard and a group of scientists, with input from the plaintiffs, said Todd Steiner, head of the Turtle Island Restoration Network.
He said the agreed-upon procedures will be announced "on a very fast track for public comment so that it can be finalized as soon as possible."
In the meantime the Coast Guard and BP promised that controlled burnings, which were halted earlier this week because of bad weather, would not be resumed before next Tuesday due to continuing rough seas in the Gulf.
They also agreed to inform plaintiffs by Tuesday as to whether qualified turtle observers will be in place before burnings resume, and "if they cannot make that assurance, we will be back before Judge Barbier," Steiner said.
The Coast Guard Admiral has said in a court filing there was no evidence that endangered turtles had perished in the fires deliberately ignited on the Gulf surface.
But environmentalists and other experts have said turtle mortality in the controlled burns is a near certainty.
The government says at least 275 controlled burns have been conducted in the Gulf since the spill, removing some 10 million gallons (37.8 million liters) of oil from the open water.
BP said in documents responding to the lawsuit that the "relief that plaintiffs are seeking ... is largely already being undertaken" by BP and the government's oil spill command.
Joining the Turtle Island Restoration Network as plaintiffs in the case, 2:10-cv-01866-KDE-DEK, are the Animal Legal Defense Fund, the Animal Welfare Institute and the Center for Biological Diversity. (Writing and additional reporting by Steve Gorman in Los Angeles; Editing by Sandra Maler)