Officials familiar with the Senate Intelligence Committee investigation also say analysts warned against U.S. domination in the region, which could increase extremist recruiting. The officials spoke on condition of anonymity because the report's declassification is not finished. It could be made public as soon as this week.
The committee also found that the warnings predicting what would happen after the U.S.-led invasion were circulated widely in government, including to the Pentagon and the Office of the Vice President. It wasn't clear whether President Bush was briefed.
A National Security Council spokesman could not immediately be reached for comment Wednesday evening.
The report comes as the administration is facing renewed criticism for failing to execute adequate post-invasion plans to stabilize Iraq after Saddam Hussein was toppled. Meanwhile, the White House has been trying to make the case that Iraq cannot be abandoned.
The committee's findings are the latest chapter in its four-year investigation into the prewar intelligence assessments on Iraq. An earlier volume, completed and released in 2004, was highly critical of the intelligence community and then-CIA Director George Tenet.
That 511-page document found widespread problems throughout U.S. spy agencies and said the intelligence community engaged in "group think" by failing to challenge the assumption that Iraq had weapons of mass destruction. Senators also found that analysts failed to explain their uncertainties to policymakers.
Yet, in predicting the effects of the U.S. invasion, the committee now finds that U.S. analysts appear to have largely been on the mark.
A former intelligence official, who spoke on condition of anonymity, said the decision to go to war had been made months before the 2003 papers were drafted and analysts had no delusions that they were going to head off military action. Rather, the official said, they hoped their warnings would be considered in the planning.
Since the release of his memoir several weeks ago, Tenet has been criticized anew for not doing more to warn Bush about the shaky Iraq intelligence and the consequences of invading.
Yet his book provided a glimpse of some of the prewar warnings about the consequences of invading Iraq.
For instance, he discusses a paper prepared for a Camp David meeting with the president in September 2002 entitled, "The Perfect Storm: The Negative Consequences for Invading Iraq." Tenet called the paper a list of "worst-case scenarios," which included anarchy and territorial breakup of Iraq and a surge of global terrorism against U.S. interests, fueled by deepening Islamic antipathy toward the United States.
He also notes that, in an early 2003 intelligence paper, analysts warned that "a post-Saddam authority would face a deeply divided society with a significant chance that domestic groups would engage in violent conflict with each other, unless an occupying force prevented them from doing so."
The paper, which is believed to figure in the Senate investigation, also noted that Iraq's long history of foreign occupation means that it has a deep dislike of occupying forces.
Since 2003, the Senate committee — led by Sen. Pat Roberts, R-Kan., and now Jay Rockefeller, D-W.Va. — has been trudging through its investigation of what went wrong, frequently slowed by politics.
Last fall, the committee released new chapters on what was learned after the invasion about Iraq's weapons of mass destruction and its links to terrorism and how information from an advocacy group, the Iraqi National Congress, crept into U.S. intelligence reporting.
While the first phase of its report was supported unanimously just before the 2004 presidential elections, the newer findings on the intelligence community's predictions about postwar Iraq have drawn dissent from Republicans. Details on the committee's vote have not yet been released.