The declassified document due for release on Friday by the Senate Intelligence Committee also explores the role of inaccurate information supplied by the anti-Saddam exile group the Iraqi National Congress.
Opposition Democrats immediately accused the Bush administration of deceiving Americans to speed the path to war, igniting a new political row in the already vitriolic run-up to November's US congressional election.
"Saddam Hussein was distrustful of al-Qaeda and viewed Islamic extremists as a threat to his regime, refusing all requests from al-Qaeda to provide material or operational support," the report said.
The assessment also dismissed administration claims that Saddam had links with al-Qaeda's leader in Iraq, Zarqawi, killed in a US raid on June 7 after unleashing a string of attacks.
"Post-war information indicates that Saddam Hussein attempted unsuccessfully to locate and capture Zarqawi, and that the regime did not have a relationship with, harbour, or turn a blind eye toward Zarqawi," the report said citing CIA intelligence.
Saddam also repeatedly rebuffed requests for meetings from al-Qaeda operatives, the report said.
Before and after the US-led 2003 invasion of Iraq Bush administration leaders used purported ties between Iraq and terrorist groups, including al-Qaeda, as part of their justification for the war.
On June 14, 2004 Vice President Dick Cheney said: "Saddam Hussein was in power, overseeing one of the bloodiest regimes of the 20th century ... he had long-established ties with al-Qaeda."
A day later, Mr Bush was asked at the White House to name the best evidence for a link between Saddam Hussein and al-Qaeda.
"Zarqawi. Zarqawi is the best evidence of connection to al-Qaeda affiliates and al-Qaeda," the president said.
On August 21, this year, Mr Bush said: "Imagine a world in which you had Saddam Hussein who had the capacity to make a weapon of mass destruction, who was paying suiciders to kill innocent life ... who had relations with Zarqawi."
The report also found that Iraq ended its nuclear program in 1991, and its ability to reconstitute it progressively declined after that date. The administration claimed prior to the invasion of Iraq that the program had been restarted.
A second committee report released on Friday probed the role of the exiled Iraqi National Congress in providing intelligence on Saddam's weapons of mass destruction programs, which was later discredited.
Democrats inserted "additional views" in the second report, accusing the White House of using "uncorroborated, unreliable and, in critical instances, fabricated" material intelligence services had deemed unreliable.
But the committee's Republican co-chair Senator Pat Roberts accused them of trying to "rewrite history."
"I believe the American people are smart enough to recognise election-year politicking when they see it," he said.
Democratic Senator John (Jay) Rockefeller said the reports showed administration allegations of a "past, present and future relationship between al-Qaeda and Iraq were wrong and intended to exploit the deep sense of insecurity among Americans" after September 11.
"The administration sought and succeeded in creating the false impression that al-Qaeda and Iraq presented a single, unified threat to the United States," he said.
Democrat Senator Carl Levin said the report was "a devastating indictment of the Bush-Cheney administration's unrelenting, misleading and deceptive attempts to convince the American people that Saddam Hussein was linked with al-Qaeda."
But White House spokesman Tony Snow, speaking before the report was released, said it contained "nothing new."
"It's, again, kind of re-litigating things that happened three years ago," he said.
"The president's stated concern this week, as you've seen, is to think, 'okay, we'll let people quibble over three years ago. The important thing to do is to figure out what you're doing tomorrow and the day after and the month after and the year after to make sure that this war on terror is won'."
The panel report is Phase II of an analysis of pre-war intelligence on Iraq. The first phase, issued in July 2004, focused on the CIA's failings in its estimates of Iraq's weapons program.