But the CIA says the panel is drawing conclusions prematurely, since the weapons hunt is continuing in Iraq.
The Washington Post says the report by the Senate Intelligence Committee will fault intelligence agencies, especially the CIA, for using too much disputed, circumstantial or single-source data in preparing its estimates of Iraq's alleged weapons programs.
However, the report may not be out until the end of the year, and committee members are still divided over how much blame to assign to the CIA, the White House or the Pentagon.
The newspaper quotes the chairman of the committee, Sen. Pat Roberts, R-Kan., saying: "the executive was ill-served by the intelligence community" and calling the intelligence at times "sloppy."
Sen. Roberts later issued a statement Friday saying the Post had mischaracterized the findings.
"The article gives the impression that the Committee has completed its review of pre-war intelligence on Iraq. It also implies that there is a completed Committee report. The Committee has not finished its review of the intelligence and has not reached any final conclusions or finished a report,'' Roberts said in the statement.
Some of the panel's criticisms concern the National Intelligence Estimate on Iraq, issued last October, which declared that "Iraq has continued it weapons of mass destruction programs" and that "Baghdad has chemical and biological weapons."
One senior intelligence expert told The Post the NIE was "hastily done in three weeks."
Bill Harlow, a spokesman for the CIA, defended the NIE, saying it "reflects 10 years of work regarding Iraq's WMD programs. It is based on many sources and disciplines, both ours and those of partners around the world."
The upcoming Senate report mirrors a similar investigation on the House side. Last month, the top Republican and top Democrat heading that House probe complained about CIA methods in a letter to agency director George Tenet.
According to The Post, the panel's report will steer blame for the intelligence miscues toward the nation's spy agencies, and away from the White House. Some critics have accused the Bush administration of misusing intelligence data.
But Democrats are resisting that shift of focus. They have won a promise that the panel will question a controversial Pentagon team, the Office of Special Plans, on how it handled intelligence leading up to the war. That office has been accused of "mining" CIA data for strands that painted the most frightening picture possible of Iraq.
"It appears to me there is a clear effort being made to blame everything on the intelligence community and steer away from anything or anybody that has to do with the administration," said Sen. Jay Rockefeller, D-W.Va.
The committee spoke to 100 people who screened data on Iraq's alleged weapons and ties to terrorist groups. Those allegations were central to the White House case for war, but seven months after the start of the war, no weapons have been found.
Since the war ended, the White House has withdrawn a claim that Iraq tried to buy uranium in Africa, and the only major discovery to date — two trailers suspected of being mobile biological weapons factories — has come into doubt.
Earlier this month, Iraq Survey Group leader David Kay said in an interim report that his search teams had uncovered some evidence of ongoing missile programs and possible plans to restart biological weapons work. But there was little evidence of work on nuclear arms or chemical weapons, or any active biological weapons work.
"It is hard to understand how the committee could come to any conclusions at this point, particularly while the efforts of Dr. David Kay in Iraq are at an early stage," Harlow said.
"The committee has yet to take the opportunity to hear a comprehensive explanation of how and why we reached our conclusions," Harlow said, adding that Tenet has requested a chance for the CIA's senior leadership to appear before the committee "to help them understand this important and complex subject."
Roberts says no analyst the committee interviewed claims to have felt pressure to change their views, but other panel members point out that supervisors were always in the room when analysts were interviewed.
In their public advocacy for war, Bush administration officials often went beyond what the CIA told them.
For example, the NIE contained caveats on nuclear activities, unmanned aerial vehicles, and Iraq's doctrine for using WMD that administration officials rarely acknowledged.
Twice in the fall of 2002, the CIA prevented White House officials from making the claim that Iraq tried to buy uranium in Africa. But the allegation made it into the president's State of the Union and other officials' public remarks. It was only withdrawn this summer.
Vice President Dick Cheney has sometimes alluded to a link between Saddam Hussein and Sept. 11 terrorist attacks that intelligence agencies have never substantiated.
A former top State Department intelligence official, Greg Thielmann, told CBS News' 60 Minutes II that contrary to what Secretary of State Colin Powell told the United Nations, Iraq didn't pose an imminent threat to anyone: "I think it didn't even constitute an imminent threat to its neighbors at the time we went to war."
President Bush has referred to the suspected biological weapons factories as actual "weapons" even though the CIA said the trailers contained no weapons material. On May 30, he told Polish television: "We've found the weapons of mass destruction."