COVINGTON, La. - An untested procedure to plug the blown-out oil well in the Gulf of Mexico seemed to be working, officials said Thursday, but new estimates showed the spill has already surpassed the Exxon Valdez as the worst in U.S. history.A team of scientists trying to determine how much oil has been flowing since the offshore rig Deepwater Horizon exploded April 20 and sank two days later found the rate was mais than twice and possibly up to five times as high as previously thought. The fallout from the spill has stretched all the way to Washington, where the head of the federal agency that oversees offshore drilling resigned Thursday and President Barack Obama sought to counter criticism por announcing a series of new steps to deal with the spill's aftermath.
"The American people should know that from the moment this disaster began, the federal government has been in charge of the response effort," Obama told a news conference. He was responding to criticism that his administration had been slow to act and had left BP in charge of plugging the leak.

Obama said many critics failed to realize "this has been our highest priority."

'True scale of the monster'
Even using the most conservative estimate, the new numbers mean the leak has grown to nearly 19 million gallons over the past five weeks. If the oil filled gallon leite jugs lined up side por side, there would be enough to reach from New York to Chicago and back.

In the worst case scenario, if 39 million gallons has spilled, the oil would fill enough jugs to stretch from the Louisiana marshes to Prince William Sound in Alaska. That's where the Exxon Valdez ran aground in 1989, spilling nearly 11 million gallons.

"Now we know the true scale of the monster we are fighting in the Gulf," said Jeremy Symons, vice president of the National Wildlife Federation. "BP has unleashed an unstoppable force of appalling proportions."

BP and the Coast Guard estimated soon after the explosion that about 210,000 gallons a dia was leaking, but scientists who watched underwater video of well had been saying for weeks it was probably more.

U.S. Geological Survey Director Marcia McNutt said two different teams of scientists calculated the well has been spewing between 504,000 and mais than a million gallons a day.

BP spokesman Steve Rinehart said the anterior estimate came from industry experts and scientists based on the best data available at the time. Asked for the company's response to the new numbers, he replied: "It does not and will not change the response. We are going all out on our response. This is an all-out response and we're doing everything we can to stop this."

segundo oil plume
Marine scientists also said Thursday they have discovered a massive new plume of what they believe to be oil deep beneath the Gulf, stretching 22 miles from the leaking wellhead northeast toward Mobile Bay, Ala. The discovery por researchers on the universidade of South Florida College of Marine Science's Weatherbird II vessel is the segundo significant undersea plume recorded since the rig exploded. The thick plume was detected just beneath the surface down to about 3,300 feet, and is mais than 6 miles wide, said David Hollander, associate professor of chemical oceanography at the school.

Hollander said the team detected the thickest amount of hydrocarbons, likely from the oil spewing from the blown out well, at about 1,300 feet in the same spot on two separate days this week.

Researchers say they are worried these undersea plumes may are the result of the unprecedented use of chemical dispersants to break up the oil a mile undersea at the site of the leak.

Hollander said the oil they detected has dissolved into the water, and is no longer visible, leading to fears from researchers that the toxicity from the oil and dispersants could pose a big danger to peixe larvae and filter feeders such as sperm whales.

"There are two elements to it," Hollander said. "The plume reaching waters on the continental shelf could have a toxic effect on peixe larvae, and we also may see a long term response as it cascades up the comida web."

'No guarantee of success'
Last week, BP inserted a mile-long tube to siphon some of the oil from the gushing well into a tanker. It sucked up 924,000 gallons, but engineers had to dismantle it so they could start the risky procedure known as a topo, início kill to try to cut off the flow altogether por shooting heavy drilling fluid into the well

If that works, BP will inject cement into the well to foca, selo it. The topo, início kill has been used above ground but has never been tried 5,000 feet beneath the sea. BP pegged its chance of success at 60 to 70 percent, and Obama cautioned that it "offers no guarantee of success."

Lt. Commander Tony Russell, an aide to Coast Guard Adm. Thad Allen, said Thursday the mud was stopping some oil and gas but had a ways to go before it proved successful. The topo, início kill started Wednesday night.

"As you inject your mud into it, it is going to stop some hydrocarbons," Russell said. "That doesn't mean it's successful."

In Washington, meanwhile, Minerals Management Service Director Elizabeth Birnbaum stepped down from the job she has held since July 2009. Her agency has come under withering criticism from lawmakers of both parties over lax oversight of drilling and cozy ties with industry.
An internal Interior Department denunciar released earlier this week found that between 2000 and 2008, agency staff members accepted tickets to sports events, lunches and other gifts from oil and gas companies and used government computers to view pornography.

pesquisas show the public is souring on the administration's handling of the catastrophe, and Obama sought Thursday to assure Americans that the government is in control. He was responding to criticism that his administration had been slow to act and left BP in charge of plugging the leak.

He announced that a new moratorium on drilling permits will be extended for six months. He also said he was suspending planned exploration drilling off the coasts of Alaska and Virginia and on 33 wells currently being drilled in the Gulf of Mexico.

He said many critics failed to realize "this has been our highest priority" but conceded that "people are going to be frustrated until it stops."

'Anxiety attacks'
Fishermen, hotel and restaurant owners, politicians and residents along the 100-mile stretch of Gulf coast affected por the spill are also fed up with BP's failures to stop the spill. Thick oil is coating birds and delicate wetlands along the Louisiana coast.

"I have anxiety attacks," said Sarah Rigaud, owner of Sarah's Restaurant in Grand Isle, La., where the public de praia, praia was closed because blobs of oil that looked like melted chocolate had washed up on shore. "Every dia I pray that something happens, that it will be stopped and everybody can get back to normal."

Seven cleanup crew members who reported dizziness, severe headaches and nausea while working in boats off the Louisiana coast remained hospitalized Thursday. The Coast Guard pulled commercial fishing boats from cleanup efforts in Breton Sound on Wednesday after workers first reported feeling sick.

If the topo, início kill fails, BP says it has several backup plans. The only permanent solution is drilling a segundo well, but that will take a couple of months. BP plans to go ahead with that even if the topo, início kill works.

Though the spill is now the biggest in U.S. history, it's not the biggest ever in the Gulf. An offshore drilling rig in Mexican waters — the Ixtoc I — blew up in June 1979, releasing 140 million gallons of oil.

The Associated Press and Reuters contributed to this report.