US President Barack Obama has ordered a tripling of manpower in coastal areas where oil has washed ashore or threatens to within 24 hours.
Speaking on a tour of oil-hit areas, Mr Obama said the US would "do whatever it takes" to help those affected.
The oil company BP says operations to seal the hole in the damaged well are continuing.
BP chief executive Tony Hayward said the outcome would not be clear for another 48 hours.
He said the new "top kill" effort - untested before at this depth of 5,000ft (1.5km) - was "going pretty well according to plan".
Mr Obama said the additional manpower would lay more booms, clean beaches and monitor stricken wildlife.
He said 20,000 people had already been deployed to contain and clean up the spill.
Doug Suttles of BP: ''We've had periods of pumping followed by periods of monitoring''
He said US Energy Secretary Steven Chu was leading a team of "the world's top scientists, engineers and experts" in devising a contingency plan should the "top kill" attempt fail.
"Our response will continue with its full force regardless of the outcome of the top-kill approach," he told reporters.
Mr Obama said he would take responsibility for "solving this crisis", though he said BP would be held financially accountable for the "enormous damage".
"I'm the president and the buck stops with me," he said.
AT THE SCENE
Mark Mardell
BBC News, Louisiana
The criticism began in Washington but the mood here in Louisiana is changing, and there is a sense of hopelessness and anger directed towards President Obama now as well as BP.
The complex relationship between the oil company and the government adds to the sense of confusion. Only BP has the equipment to stop the leak and the law says it is responsible for the clear-up. But there is a growing sense that the president hasn't visibly taken control.
His trip to Grand Isle is designed to deal with that but its very brevity, less than two hours here, may undermine the intention.
This is the first major crisis that has happened on Mr Obama's watch and his handling of it has not increased his reputation for competence, leadership or, strangely, empathy.
Mardell: Louisiana's frustration
"I give the people of this community and the entire gulf my word that we're going to hold ourselves accountable to do whatever it takes for as long as it takes to stop this catastrophe, to defend our natural resources, to repair the damage and to keep this region on its feet."
Earlier on the tour, Mr Obama visited a beach guarded by a protective boom, and was seen stooping to inspect the sand and picking up a handful of tar balls.
Thousands of barrels of oil have been leaking into the Gulf of Mexico after a Deepwater Horizon rig exploded and sank last month, killing 11 employees.
The thick crude oil has already permeated more than 110km (70 miles) of Louisiana's coastline, threatening fragile wetlands and putting the vital fishing industry at risk.
Earlier, Mr Hayward has said that BP engineers had successfully completed a second phase of the "top kill" procedure - pumping in debris, known as a "junk shot" - which would next allow them to pump in more heavyweight mud.
If the mud works in stopping the flow, BP can then pour cement to seal the well for good.
New estimates from a panel of US scientists said at least 12,000 barrels (504,000 gallons) were leaking into the gulf every day, making it the worst spill in US history.
In a shake-up of the offshore oil industry, Mr Obama on Thursday suspended test drilling on 33 rigs in the Gulf of Mexico, as well as halting exploratory deepwater drilling for another six months.
In addition, he cancelled the sale of some offshore leases off the coasts of Alaska and Virginia.
Correspondents say the move marks a shift in policy since March, when President Obama gave the go-ahead to widen the scope for offshore drilling in order to reduce dependency on oil imports.
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