VENICE, Louisiana (Reuters) - U.S. officials on Saturday conceded it is "inevitable" that oil from an uncontrolled leak in the Gulf of Mexico will hit the U.S. coast, threatening an environmental and economic catastrophe.
"There's enough oil out there that it is logical to think it will hit the shoreline. It's just a question of where and when," said U.S. Coast Guard Admiral Thad Allen. "Mother Nature gets a vote in this."
President Barack Obama will visit the region on Sunday, ramping up efforts to control what has the makings of an environmental disaster and deflect criticism that his administration could have been quicker in responding to the spill.
Coastline from Louisiana to Florida is threatened by the slick, estimated to be some 130 miles by 70 miles in size.
Major shipping channels, key fishing areas, national wildlife refuges and popular beaches are in the path of the oily soup. So far, vital shipping lanes leading to the Mississippi River and huge Gulf Coast ports have not been affected, officials said.
The oil gushing unchecked from a ruptured deepwater well about 42 miles off the Louisiana coast is being pushed northward by heavy but shifting winds. A "sheen" is approaching parts of the Louisiana coast, Allen said.
In the first sign that the spill has affected U.S. offshore energy production, the Minerals Management Service said on Saturday two U.S. offshore Gulf of Mexico production platforms had been shut down and a third was evacuated as a safety precaution. Further shutdowns were possible, it added, but the output affected so far was very small.
The leak, which followed a rig explosion and sinking last week, has forced Obama to suspend politically sensitive plans to expand offshore oil drilling, unveiled last month partly to woo Republican support for climate legislation.
Obama's administration is piling pressure on London-based BP Plc, the owner of the blown-out well, to do more to plug the flow of oil and contain the spreading slick. The cost of the cleanup, and the potential damage that could be inflicted by the spill, are estimated in the billions of dollars.
BP Chief Executive Tony Hayward was traveling to the U.S. on Saturday to oversee the emergency cleanup operation.
BP, the Coast Guard, the U.S. military and volunteers have been trying desperately to disperse, block and stem the oil slick both above and under water.
The various surface dispersal efforts have shown some promise, but "the focus has got to be to stop it at the source," said Obama adviser John Brennan.
Crude oil is pouring out at a rate of up to 5,000 barrels (210,000 gallons or 795,000 liters) a day, according to government estimates, but experts said the quantity of crude escaping was difficult to measure and could be higher.
The spill response center staffed by BP and U.S. government officials said crews worked through the night using an underwater robot to aim thousands of gallons (liters) of dispersant at the leaking oil beneath the surface.
Other options to try to cap or seal the well, or even simply reduce the oil flow, are seen taking weeks or months.
Above the surface, several hundred boats and planes were also struggling to contain the slick and the Coast Guard worked to extend long barriers of containment booms in an effort to stop the oil from soiling the shore.
But forecaster AccuWeather.com said deteriorating weather and rough seas were hampering cleanup crews.
A Reuters photographer who traveled in a plane that flew over the Louisiana coast saw some boom barriers broken up by the wind and waves, and the booms washed up on the coast.
Louisiana, Mississippi, Alabama and Florida have all declared states of emergency, and shrimpers, fishermen and local residents in several states have rushed to file lawsuits against the companies that operated the rig.
Obama, no doubt mindful of public criticism of President George W. Bush's handling of the 2005 Hurricane Katrina disaster, on Friday sent senior officials to check on the efforts to fight the slick.
In an editorial on Saturday, the New York Times said there were unanswered questions about the spill.
"The company, BP, seems to have been slow to ask for help, and, on Friday, both federal and state officials accused it of not moving aggressively or swiftly enough," it said. "Yet the administration should not have waited, and should have intervened much more quickly on its own initiative."
Obama and U.S. officials have increasingly stressed the first responsibility lies with BP. Interior Secretary Ken Salazar met with BP executives and said he told them to "work harder and faster and smarter to get the job done."
"BIG OIL ON TRIAL"
Douglas Brinkley, a professor at Rice University in Houston, said he believed the Obama administration was holding back from criticizing BP more because it needed the company to help seal the well.
"Once the hole is plugged you are going to see the federal government rake British Petroleum over the coals ... Big Oil will be put on trial in the same way that Goldman Sachs is getting put on trial," Brinkley said.
BP's Hayward promised an aggressive cleanup campaign and said the company would compensate those affected.
Officials in Louisiana's Mississippi Delta said on Friday a thin "oil sheen" had reached barrier islands.
Off the Louisiana coast, miles and miles of boom had been laid. BP, working with the Coast Guard, was also using specialized boats with oil-skimming equipment and private fishermen have been contracted to help with the cleanup.
About 6,000 Louisiana National Guard troops were mobilized and two Air Force planes were sent to spray dispersant.
Experts said there was little hope BP would succeed with a quick fix to cap the well, which is very deep at 5,000 feet down on the sea bed. BP hopes to use a giant funnel that would catch the oil and channel it to a tanker ship.
But that would take four weeks. If the funnel does not work, BP will have to try stemming the flow by drilling a relief well, which would take two to three months.
"At 5,000 barrels a day, in two months' time it's going to be a bigger spill than the Exxon Valdez," said Tyler Priest of the University of Houston's Bauer College of Business. He was making a comparison with the 1989 Exxon Valdez incident, the worst U.S. oil spill on record.
The Obama administration has said no new offshore drilling areas would be allowed until after a review of the spill.
The Gulf Coast and its marshlands are home to hundreds of species of wildlife, including manatees, sea turtles, dolphins, porpoises, whales, otters, pelicans and other birds. The wetlands are also a stopover for millions of migrating birds.
The Gulf is also one of the world's most fertile seafood grounds, teeming with shrimp, oysters, mussels, crabs and fish. It supports a $1.8 billion industry second only to Alaska.
(Additional reporting by Chris Baltimore  and Kristen Hays in Houston, Tom Bergin  in London, Carlos Barria  in Venice, Louisiana, Phil Stewart  in Washington, Joshua Schnyer and Rebekah Kebede  in New York; Writing by Pascal Fletcher  and Ros Krasny ; editing by Eric Beech )