The rare criticism by career officials on Wednesday was a direct challenge to one of Bush's main arguments for re-election.
"We all believe that current administration policies have failed in the primary responsibilities of preserving national security and providing world leadership," said a statement signed by the 27 retired officials. "We need a change."
The tough rebuke came from a group that included members of both major political parties, a former CIA director, two former ambassadors to the Soviet Union and a retired chairman of the military Joint Chiefs of Staff.
The Bush administration denied it had forsaken diplomacy in favour of force, saying it won four unanimous Security Council resolutions on Iraq and cast the group's stand as "political."
"If this is a political statement ... and this is their point of view, I disagree," US Secretary of State Colin Powell told Aljazeera Channel in an interview.
'US not isolated'
"We are in Iraq with many other nations that are contributing troops. Are we isolated from the Brits, from the Poles, from the Romanians, from the Bulgarians, from the Danes, from the Norwegians?" he asked.
Colin Powell disagreed with the
group's "political statement"
In attacking Bush's national security record, the group challenged a core Bush argument for his re-election against Democrat Senator John Kerry, that the Iraq war has made America safer and that Bush is an effective wartime president.
"Our security has been weakened," the group said.
The former officials, some of whom said they had voted for Bush in 2000, said the Republican president manipulated intelligence on Iraq to lead the US into an "ill-planned and costly war from which exit is uncertain."
Bush has maintained an "overbearing" approach to foreign policy that relied excessively on military power, spurned the concerns of traditional US allies and disdained the United
Nations, the group said.
"It justified the invasion of Iraq by manipulation of uncertain intelligence about weapons of mass destruction, and by a cynical campaign to persuade the public that Saddam Hussein was linked to al Qaeda and the attacks of 11 September," it said. "The evidence did not support this argument."
"Never in the two and a quarter centuries of our history has the United States been so isolated among the nations, so broadly feared and distrusted," it added.