NEW ORLEANS — Oil leaking from a sunken drilling rig in the Gulf of Mexico oozed slowly toward the coast Monday, endangering hundreds of miles of marshes, barrier islands and white sand beaches in four states from Louisiana to Florida.

The areas, home to dolphins, sea birds, prime fishing grounds and tourist playlands, could be fouled later this week if crews can't cut off an estimated 160,000 litres a day escaping two leaks in a drilling pipe about 1,500 metres below the surface.

The rig Deepwater Horizon exploded April 20 and sank two days later. Eleven of the 126 workers on board at the time are missing and presumed dead; the rest escaped. The cause of the explosion has not been determined and oil has been leaking ever since.

As of Monday afternoon, it covered an area that was 77 kilometres long by 63 kilometres wide.

Crews used robot submarines to activate valves in hopes of stopping the leaks, but they may not know till Tuesday if that strategy will work. BP had also mobilized two rigs to drill a relief well if needed. Such a well could help redirect the oil, though it could also take weeks to complete, especially at that depth.

The spill, moving slowly north and spreading east and west, was about 50 kilometres from the Chandeleur Islands off the Louisiana coast Tuesday. The National Oceanographic and Atmospheric Administration said it would likely be several days before any oil reaches the coast.

George Crozier, oceanographer and executive director at the Dauphin Island Sea Lab in Alabama, said he was studying wind and ocean currents driving the oil. He said Pensacola, Florida, is likely the edge of the threatened area.

"I don't think anybody knows with confidence what the effects will be," Crozier said. "We've never seen anything like this magnitude."

In Louisiana, Gov. Bobby Jindal asked the Coast Guard to deploy oil containment booms in the Pass A Loutre wildlife area, a 47,000-hectare preserve that is home to alligators, birds and fish near the mouth of the Mississippi River.

In Mississippi, Gov. Haley Barbour said he has spoken with the Coast Guard mission commander, Rear Adm. Mary Landry but was uncertain what steps his state might take to protect its beaches.

"It's a real difficulty in trying to determine what defences will be effective," he said.

A fleet of boats and containment equipment was working to corral and skim oil from the surface of the Gulf late last week. But a weather system that spawned deadly tornadoes in Louisiana and Mississippi and heavy seas over the weekend forced crews to suspend their efforts.

Coast Guard Petty Officer Connie Terrell said 32 vessels are waiting for conditions to improve to resume cleanup.

The Deepwater Horizon, owned by Transocean Ltd. and operated by BP Plc., was drilling about 65 kilometres off the delta of the Mississippi River when it exploded.