Washington ? A damning report by a presidential commission concluded Thursday that the United States knows “disturbingly little” about nuclear and biological threats from dangerous adversaries, years after the Sept. 11, 2001, attacks and the nation’s intelligence missteps on Iraqi weapons.

Urging dramatic changes in the U.S. spy agencies, the commission called crucial intelligence judgments on Iraq “dead wrong” and said the flaws it found “are still all too common.”

Though he initially opposed the panel’s creation, President Bush promised immediate action at a news conference with retired Judge Laurence Silberman, a Republican, and former Democratic Sen. Charles Robb of Virginia, the commission’s co-chairmen.

“To win the war on terror, we will correct what needs to be fixed,” Bush said.

The commission offered 74 recommendations aimed at changing the structure and culture of the nation’s 15 spy agencies. It called for more clarity in the powers of the newly created national intelligence director, an overhaul of national security efforts in the Justice Department and dozens of changes in intelligence collection and analysis.

“There is no more important intelligence mission than understanding the worst weapons that our enemies possess, and how they intend to use them against us,” the commission said. “These are their deepest secrets, and unlocking them must be our highest priority.”

The report, approved unanimously by the bipartisan nine-member panel, followed the failure of U.S. inspectors in Iraq to turn up any weapons of mass destruction. The existence of weapons stockpiles — detailed in dozens of intelligence reports before the March 2003 invasion — was the administration’s leading argument for toppling Saddam Hussein.

Numerous blue-ribbon panels since the 9-11 attacks have investigated intelligence shortfalls. This commission — in the bluntest of terms — provided the most comprehensive look so far.

The report painted a picture of a clumsy intelligence apparatus struggling to penetrate Iraqi operations and wrongly concluding that Saddam had weapons capable of causing catastrophic damage. Commissioners found intelligence collectors didn’t provide enough information or were deceived by discredited sources and analysts relied on old assumptions about Saddam’s intentions and overstated their conclusions.

“On a matter of this importance, we simply cannot afford failures of this magnitude,” said the report, which exceeded 600 pages.

Robb and Silberman said they found no evidence that senior Bush administration officials sought to change the prewar intelligence in Iraq. The report was silent on whether the administration manipulated the data for political purposes, as Democrats have contended, with commission members saying they were not empowered to examine that.

Underscoring the political divide, Democrats used the findings to demand faster changes and to point fingers.

“The investigation will not be complete unless we know how the Bush administration may have used or misused intelligence to pursue its own agenda,” said House Minority Leader Nancy Pelosi, D-Calif.

The commission warned John Negroponte, whom Bush nominated to coordinate the spy community, of the intelligence agencies’ “almost perfect record of resisting external recommendations.”

It said the CIA and the Defense Department’s intelligence agencies “are some of the government’s most headstrong agencies. Sooner or later, they will try to run around — or over” the new director.