"They dare not admit the truth lest they look like complete fools for launching our country into a reckless, discretionary war against a nation that posed no immediate threat to us whatsoever," Gore, the former vice president who lost the presidency to Mr. Bush in 2000, said during a speech at Georgetown University Law Center.
Republicans responded that the Democrat's assertions were false and out of touch.
Ken Mehlman, the Bush re-election campaign chairman, admonished Gore for delivering "another gravely false attack" and the Republican National Committee contended he was out of touch.
"Al Gore's history of denial of the threat of terrorism is no less dangerous today in his role as John Kerry's surrogate than it was in the 1990s in his role as vice president, a time when Osama bin Laden was declaring war on the United States five different times," RNC spokesman Jim Dyke said in a statement.
Mostly sidelined from the presidential race, Gore emerges every few months with another stinging review of the Bush administration. The former vice president, who has grown irate and bellowed in previous appearances, took a more tempered but highly sarcastic tone on Thursday.
Gore accused President Bush and Vice President Dick Cheney of deliberately ignoring warnings from international intelligence services, the CIA and the Pentagon before the Iraq war that their claim of a link between al Qaeda and Saddam was false.
With a smirk, Gore then added: "So when the bipartisan 9/11 commission issued its report finding 'no credible evidence' of an Iraq-al-Qaeda connection, it should not have come as a surprise. It should not have caught the White House off guard."
The independent, bipartisan commission looking into the terrorist attacks found "no credible evidence" of a link between the events of Sept. 11, 2001, and Iraq. As to an Iraq-al-Qaeda connection, the commission found there was no apparent "collaborative relationship."
Gore said Mr. Bush and Cheney won't acknowledge what he called their fabrication because of the "harsh political consequences" of admitting there's no evidence of a link. "If they believe these flimsy scraps, then who would want them in charge? Are they too dishonest or too gullible? Take your pick," Gore said.
Gore also accused Mr. Bush of abusing his presidential powers by invading Iraq without a war declaration from Congress, allowing Americans deemed "unlawful enemy combatants" to be held without being charges, and authorizing "what plainly amounts to the torture of prisoners."
He also called on the administration to disclose all of its interrogation policies — including those used in Iraq and Afghanistan, and by the CIA — and analyses about them.
"We deserve to know what and why it's being done in our name," Gore said to applause.
Still popular among Democrats, Gore is an important ally for Kerry because he can criticize Mr. Bush in harsher terms than Kerry, this year's Democratic presidential candidate. Aides said Kerry must temper his critiques of the president to avoid alienating the independent and swing voters who will influence the outcome on Nov. 2.
Gore's staff, in a typical heads-up, told Kerry's campaign a few days ago that he would be giving a speech on Iraq. The campaign did not know the details until Gore's staff released its media advisory this week.
The former vice president does not clear his speeches or schedule through Kerry's staff, but Kerry's aides welcome his attacks on Mr. Bush. They say Gore's red-meat rhetoric helps fire up the Democratic base and underscores criticisms Kerry makes in a more muted fashion.