WASHINGTON - As BP neared a fix that's expected to kill for good the runaway well that's wreaked economic and environmental catastrophe in the Gulf of Mexico, the government Monday said that 10 to 12 times the amount of oil had been flowing from the well than it originally thought.

Oil and gas leaking from the BP's ruptured well is sprayed with toxic dispersant in this image captured from a BP live video in the Gulf of Mexico on July 15, 2010 New estimates released Monday by a government-led team of scientists found that as much as 62,000 barrels of oil were leaking from the well each day at its peak - far beyond the initial estimate of 5,000 barrels a day and more in line with what scientists told McClatchy it was.

The new estimates raise questions about whether the early response ever anticipated the disaster's actual size and scope. The well gushed an estimated 4.9 million barrels for nearly three months before BP put in place a temporary cap 18 days ago.

The government now estimates that 53,000 barrels were leaking each day before BP installed the cap. Only 800,000 barrels - about 16 percent of the total - was captured before flowing into the ocean.

Now, BP is finalizing plans to begin what's called a "static kill," a process that would force down any remaining oil and gas in the well by pumping heavy drilling mud into it.

"We'll just be slowly pumping the mud in initially and it will gradually build up pressure," BP's Kent Wells said Monday during a technical briefing. "We'll be carefully monitoring the pressures and the volumes. The team will be looking and making sure we do everything to get this well killed, if at all possible."

That procedure is expected to begin Tuesday and could stretch into Wednesday. If it works - and the White House said it is "watching cautiously" - BP will move quickly this week to begin cementing the well closed permanently.

The company still must decide how best to cement the well closed: from the top, or through one of the relief wells currently being drilled. There's still some uncertainty about the conditions deep inside the well, and until they pump mud into it, company officials won't know the safest way to proceed, said Thad Allen, the top federal official in charge of the spill response. It would make him most comfortable to close the well in from the bottom using the relief wells they've drilled, Allen said.

"I think everybody would like to have this thing ended as soon possible," Allen said, "but my duty as the National Incident Commander is to give you my best view. It may be a little conservative, but I think we need to understand: We don't know the condition of the well until we start to put mud in it."

Meanwhile, both Allen and the Environmental Protection Agency on Monday defended the safety of chemicals credited with breaking up the oil into tiny droplets and dispersing it into the Gulf. The EPA said Monday those dispersants hastened the decomposition of the oil, a process that may also have kept vast quantities of oil from fouling the shoreline. BP, which used more than 1.84 million gallons of dispersants, stopped applying them shortly after it put the cap in place.

The EPA said Monday its new study found the dispersants used to break up oil in the Gulf are no more toxic when mixed with oil than the oil is on its own.

Dispersants were used as a "last resort and necessary tool, when all other measures were not adequate" against the oil, said Paul Anastas, the EPA's assistant administrator for research and development. Oil, Anastas said, was "enemy No. 1."

So far, the government's monitoring data shows no accumulation of dispersant in marine life that was tested, including on juvenile shrimp and small fish that are found in the Gulf and are commonly used in toxicity testing.

All eight dispersants were found to be less toxic than the dispersant-oil mixture to both species. Oil was more toxic to shrimp than the eight dispersants when tested alone. Oil alone had similar toxicity to shrimp as the dispersant-oil mixtures, with exception of one other dispersant, which was found to be more toxic than oil.

However, Anastas also said there's "ongoing monitoring" by a number of federal agencies, including the Food and Drug Administration, to ensure the food chain is not affected. The EPA hasn't found any dispersant "away from the wellhead," Anastas said, including in sediment or near coastal wetlands.

He called it "interesting to see that the dispersant/oil mixture was about the same toxicity as oil alone. That shows us that the effect of oil plus dispersant seemed to be a wise decision and that oil itself is the hazard we're concerned about."

Often, Allen said, the government was making decisions "without complete information, and sometimes under conditions of uncertainty because we have never used dispersants at this level before."

"That was done, and to the extent there's an issue about it, I'm the National Incident Commander and I'm accountable," he said.

Yet scientists say many questions remain about the use of the chemicals, and congressional investigators still plan a hearing Wednesday to examine why the U.S. Coast Guard allowed BP to continue using dispersants in the face of multiple warnings from the EPA.

"The Coast Guard proceeded to approve use of surface dispersants 74 times over a period of 48 days," said Rep. Ed Markey, D-Mass. "That is not 'rare' by anyone's understanding of the word, and it raises questions regarding whether an excessive amount of surface dispersant may have been used."

Jerald Ault, a professor at the University of Miami's Rosenstiel School of Marine and Atmospheric Science, said he's worried about the potential cascading effects of the dispersant in marine life and how it could effect physical growth, reproduction and mortality. Some of the effects on the environment may not play out for some time, he said.

"It's good to say it's in the same ballpark as oil, but from where I sit, that's one plus one," he said. "I buy that it's a tradeoff, but the question is: 'What are the consequences of the tradeoff?' I'm not sure we have the ability to determine that at this point."

Other scientists have linked subsea plumes of oil to the well, and fear that the tiny droplets 4,300 feet below the surface of the Gulf will be more readily absorbed and ingested by marine animals.

"These particles of dispersed oil are small enough to be easily absorbed by filter feeding animals such as oysters, and also absorbed into the bodies of crabs and shrimp," said Gina Solomon, a senior scientist with the Natural Resources Defense Council. "Big globs of oil wouldn't get into these creatures as easily. That may mean a higher likelihood of contamination in the food chain, which would be bad news for predators in the ocean and also maybe for humans if seafood becomes more contaminated with oil residues."