The Obama administration lost the public trust and may have sabotaged clean-up operations in the Gulf of Mexico by grossly underestimating the amount of oil gushing from BP's broken Macondo well, according to a White House commission appointed to investigate the spill.

In a scathing critique of the administration's handling of the disaster, the two co-chairs of the commission yesterday said government officials made a serious blunder by releasing early estimates of the spill that were about 60 times too low.

"It's a little bit like Custer underestimating the number of Indians on the other side of the hill and paying a price for that," Bob Graham, a former Democratic senator from Florida, told reporters.

Government agencies have come under sustained assault from independent scientists for initial estimates that put the size of the spill as low as 1,000 barrels a day – even as footage from the ocean floor showed a huge cloud of oil and gas billowing out of the BP well. A team of scientific experts assembled by the government eventually raised the estimate to more than 60,000 barrels a day.

In testimony yesterday, the coast guard commander Admiral Thad Allen insisted the underestimates had had no effect on the response. "The answer is no," Allen said. "We assumed at the outset this would be a catastrophic event."

But Allen's assertion made little headway with the other co-chair of the commission. "I would assume that it's common sense that a flow rate will determine how many skimmers you think you need, how many thousand feet of boom you bring into the area, what you are going to do with respect to dispersants," said William Reilly, who served as chairman of the Environmental Protection Agency under the first President Bush. "How do you deploy your resources if you don't know how serious the threat is?"

The low estimate may also have encouraged BP to take the ultimately unsuccessful step of attempting to cap the well with a giant dome. "I think it did have an impact … on the issue of the containment technology," Graham said.

The charges that government officials badly misjudged or misrepresented the gravity of the spill are extremely sensitive for the Obama administration, which claims repeatedly that its environmental policies are rooted in sound science.

Graham and Reilly said the disconnect between official assertions and the footage from the sea bed badly undermined public confidence in the oil spill response.

"I think it set a context for public scepticism about future information," said Graham.That scepticism rose again last month when government agencies produced a report saying about 75% of the oil had been captured, burned, dissolved or dispersed.

Bill Lehr, a senior scientist for the National Oceanic and Atmospheric Administration, stood by the report yesterday.

The authority of that report was also challenged when a leading oceanographer told the commission that more than half of the oil that spilled into the Gulf was now buried along the coast or on the sea floor.

"Over 50% of the total discharge is a highly durable material that resists further dissipation," Ian MacDonald, a scientist at Florida State University told the commission.

"Much of it is now buried in marine and coastal sediments. There is scant evidence for bacterial degradation of this material prior to burial."