NEW YORK — Senator John Kerry said Monday that mistakes by President George W. Bush in invading Iraq could lead to unending war and that no responsible commander in chief would have begun the war knowing Saddam Hussein didn't possess weapons of mass destruction and wasn't an imminent threat to the United States.

"Yet today, President Bush tells us that he would do everything all over again, the same way. How can he possibly be serious?" the Democratic presidential candidate said at New York University.

Kerry, a fourth-term Massachusetts senator, voted to give Bush authority to wage the war and he said in August he still would have voted that way had he known there were no weapons of mass destruction in Iraq.

The Democrat makes a distinction between his voting to grant a president war-making authority as a member of the Senate and Bush, as commander in chief, actually taking that fateful step. Republicans have accused Kerry of waffling on the war.

Kerry said Monday, "Is he really saying to Americans that if we had known there were no imminent threat, no weapons of mass destruction, no ties to al-Qaida, the United States should have invaded Iraq? My answer is resoundingly no because a commander in chief's first responsibility is to make a wise and responsible decision to keep America safe."

"Saddam Hussein was a brutal dictator who deserves his own special place in hell," Kerry said. "But that was not, in itself, a reason to go to war. The satisfaction we take in his downfall does not hide this fact: We have traded a dictator for a chaos that has left America less secure."

Bush campaign spokesman Steve Schmidt said Kerry's goal of pulling U.S. troops out of Iraq in his first term sends "a clear signal of defeat and retreat to America's enemies that will make the world a far more dangerous place."

Kerry's speech was timed one day ahead of Bush's scheduled address to the United Nations General Assembly in New York -- and with Kerry having lost ground in opinion polls on the issue of fighting terrorism after gaining at this summer's Democratic convention and shortly thereafter. Bush planned to strike back at Kerry's increasingly aggressive criticism on Iraq, aides said.

Kerry said Monday that Bush's invasion of Iraq has created a crisis that could lead to unending war and has raised questions about whether Bush's judgment is up to presidential standards. He offered his own four-point plan starting with pressing other countries for help.

Get more help from other countries.

Provide better training for Iraqi security forces.

Provide benefits to the Iraqi people.

Ensure that democratic elections can be held next year as promised.

"If the president would move in this direction ... we could begin to withdraw U.S. forces starting next summer and realistically aim to bring all our troops home within the next four years," Kerry said.

Bush's mistakes, Kerry said, "were not the equivalent of accounting errors. They were colossal failures of judgment -- and judgment is what we look for in a president."

Kerry contended that Bush has not been honest about the war's rationale or costs. He said the president's decision to go to war against Iraq has distracted from a greater threat to the United States -- more terrorist attacks.

"In Iraq, this administration has consistently over-promised and underperformed. This policy has been plagued by a lack of planning, an absence of candour, arrogance and outright incompetence. And the president has held no one accountable, including himself," Kerry said.