GALLIANO, Louisiana (AFP) – Waves of crude oil swept onto Gulf shores Tuesday as energy giant BP prepared for a desperate effort to plug a massive leak that is threatening an environmental disaster.

With the political fallout from the leak mounting, BP engineers laid plans to stifle the leak using a method known as a "top kill" that would see heavy drilling fluids, then cement, injected into the well.

The British oil firm's chief operating officer Doug Suttles said the operation which has already been delayed would now take place Wednesday.

He told CNN that the bid, using robotic submarines on the seabed, had a six or seven out of 10 chance of working.

If the "top kill" effort fails, relief wells to divert the flow and allow the leaking well to be sealed won't be ready until August at the earliest, meaning tens of millions more barrels of crude could stream into the Gulf of Mexico.

BP's chief executive Tony Hayward has admitted he was "gutted" that oil was now starting to clog fragile Louisiana wetlands, as heartrending footage emerged of helpless sea birds slimed by thick, pernicious crude.

Interior Secretary Ken Salazar betrayed simmering frustration inside the Barack Obama administration when he branded the disaster "a BP mess, a horrible mess, a massive environmental mess," during a trip to Louisiana.

Salazar had Sunday threatened to push BP "out of the way" if it was not up to the job of stopping the leak, but Obama's pointman on the disaster admitted the government had few options.

However Coast Guard chief Thad Allen said rebuffing BP may not work, since the US government lacked the expertise and equipment needed to stop the leak 5,000 feet (1,500 meters) under water.

"To push BP out of the way would raise a question -- to replace them with what?" Allen said, revealing that he had consulted another major oil firm on the situation, and been satisfied BP was doing everything that could be done.

Allen said he was frequently directly on the phone to Hayward, who he said clearly understood his instructions and carried them out.

White House spokesman Robert Gibbs meanwhile said Obama would take questions from the media after getting a report on Thursday from Salazar on whether the disaster impacted his plans to expand offshore drilling.

And at BP, "they have every impetus... to try to seal off this leak and they're working hard to do it. And we're working with them," senior White House advisor David Axelrod told CNN.

"All the scientists within our government are a part of their strategic team in dealing with this. The Coast Guard has been on the scene from the beginning," Axelrod said.

The slick was spawned by an explosion on a BP-leased Deepwater Horizon rig on April 20, which killed 11 workers.

Over a month after the accident, Obama's opponents have begun to take swings at the White House over its response, and local politicians have complained requests for resources have not yet been met.

Louisiana Governor Bobby Jindal, a Republican, pleaded for sand barriers to be constructed to protect the coast, and told grim tales of birds unable to fly because their feathers were fused together by oil.

Jindal wants to use dredgers to create barrier islands between the encroaching oil and wetlands, but the federal government is still studying whether the idea, which could take weeks to enact, would work.

Like the US government, BP intensified its PR offensive, taking out ads in major US newspapers and pledging up to 500 million dollars to study the impact of the spill.

"I think this is clearly a major reputational issue for BP," Hayward said in Port Fourchon in southern Louisiana, contradicting earlier statements in which he said the environmental impact would be "very, very modest."

"It's clear that the defense of the shoreline, at this point, has not been successful," Hayward said.

"I feel devastated by that, absolutely gutted. What I can tell you is that we are here for the long haul. We are going to clean every drop of oil off the shore."