President Obama's administration underestimated the amount of oil leaking after the BP disaster as well as the effect of the spill after the damaged well was capped, independent government investigators said.
The repeated underestimation of what became the biggest offshore oil spill in US history contributed to public skepticism about the efficacy of the administration's response, they said.
The strongly worded report was written by staff researchers and presented to the national commission, which has been tasked by Obama with presenting findings by January 2011 on the world's worst-ever oil disaster.
"The federal government created the impression that it was either not fully competent to handle the spill or not fully candid with the American people about the scope of the problem," it said.
Shortly after the BP oil rig exploded on April 20, the Coast Guard estimated that a relatively manageable 1,000 barrels a day was flowing into the Gulf of Mexico.
The report, citing interviews conducted with government officials, suspected the Coast Guard was simply relaying figures provided by BP without further documentation.
By August, Energy Secretary Steven Chu estimated that 62,000 barrels a day had in fact been gushing into the Gulf in the early stages, declining slightly to 53,000 barrels by the time the well was capped in July.
The White House hit back at the report, saying that senior officials were clear from early in the disaster that the oil flow could be worse than estimated.
The White House said that Interior Secretary Ken Salazar and Thad Allen, the retired admiral in charge of the response, both stated in early May that a worst-case scenario could be more than 100,000 barrels a day.
"The federal government response was full force and immediate, and the response focused on state and local plans and evolved when needed," a White House statement said.
"As directed by the president, the response was based on science, even when that pitted us against BP or state and local officials, and the response pushed BP every step of the way," it said.
The report found no evidence that operations were scaled back due to low estimates, saying that responders insisted they acted in line with worst-case scenarios.
"Even if responders are correct, however, loss of the public's trust during a disaster is not an incidental public relations problem," the report said.
"The absence of trust fuels public fears, and those fears in turn can cause major harm," it said, adding that the public may be now be less confident in government assurances that Gulf seafood is safe.
The BP disaster sullied hundreds of miles of coastline from Texas to Florida, killing wildlife and devastating key local industries such as tourism and fishing. Eleven workers died in the initial explosion.
US authorities last week shut down the special command center headed by Allen after the well was permanently sealed.
