Washington ? President Bush and Vice President Dick Cheney conceded Thursday in the clearest terms yet that Saddam Hussein had no weapons of mass destruction, even as they tried to shift the Iraq war debate to a new issue — whether the invasion was justified because Saddam was abusing a United Nations oil-for-food program in Iraq.

Ridiculing the Bush administration’s evolving rationale for war, Democratic presidential candidate John Kerry shot back: “You don’t make up or find reasons to go to war after the fact.”

Cheney brushed aside the central findings of chief U.S. weapons hunter Charles Duelfer — that Saddam not only had no weapons of mass destruction and had not made any since 1991, but that he had no capability of making any either — while Bush unapologetically defended his decision to invade Iraq.

“The Duelfer report showed that Saddam was systematically gaming the system, using the U.N. oil-for-food program to try to influence countries and companies in an effort to undermine sanctions,” Bush said as he prepared to fly to campaign events in Wisconsin. “He was doing so with the intent of restarting his weapons program once the world looked away.”

Duelfer found no formal plan by Saddam to resume WMD production, but the inspector surmised that Saddam intended to do so if U.N. sanctions were lifted. Bush seized upon that inference, using the word “intent” three times in reference to Saddam’s plans to resume making weapons.

This week marks the first time that the Bush administration has listed abuses in the oil-for-fuel program as an Iraq war rationale. But the strategy holds risks because some of the countries that could be implicated include U.S. allies, such as Poland, Jordan and Egypt. In addition, the United States itself played a significant role in both the creation of the program and how it was operated and overseen.

For his part, Cheney dismissed the significance of Duelfer’s central findings, telling supporters in Miami, “The headlines all say ‘no weapons of mass destruction stockpiled in Baghdad.’ We already knew that.”

The vice president said he found other parts of the report “more intriguing,” including the finding that Saddam’s main goal was the removal of international sanctions.

“As soon as the sanctions were lifted, he had every intention of going back” to his weapons program, Cheney said.

The report underscored that “delay, defer, wait, wasn’t an option,” Cheney said. And he told a later forum in Fort Myers, Fla., speaking of the oil-for-food program: “The sanctions regime was coming apart at the seams. Saddam perverted that whole thing and generated billions of dollars.”

Yet Bush and Cheney acknowledged more definitively than before that Saddam did not have the banned weapons that both men had asserted he did — and had cited as the major justification before attacking Iraq in March 2003.

Bush has recently left the question open. For example, when asked in June whether he thought such weapons had existed in Iraq, Bush said he would “wait until Charlie (Duelfer) gets back with the final report.”

In July, Bush said, “We have not found stockpiles of weapons of mass destruction,” a sentence construction that kept alive the possibility the weapons might yet be discovered.

On Thursday, the president used the clearest language to date nailing the question shut:

“Iraq did not have the weapons that our intelligence believed were there,” Bush said. His words placed the blame on U.S. intelligence agencies.

In recent weeks, Cheney has glossed over the primary justification for the war, most often by simply not mentioning it. But in late January 2004, Cheney told reporters in Rome: “There’s still work to be done to ascertain exactly what’s there.”

“The jury is still out,” he told National Public Radio the same week, when asked whether Iraq had possessed banned weapons.

Duelfer’s report was presented Wednesday to senators and the public with less than four weeks left in a fierce presidential campaign dominated by questions about Iraq and the war on terror.

In Bayonne, N.J., Democratic vice presidential candidate John Edwards on Thursday called “amazing” Cheney’s assertions that the Duelfer report justified rather than undermined Bush’s decision to go to war, and he accused the Republican of using “convoluted logic.”

Kerry, in a campaign appearance in Colorado, said: “The president of the United States and the vice president of the United States may well be the last two people on the planet who won’t face the truth about Iraq.”

A short time later, while campaigning in Wisconsin, Bush angrily responded to Kerry’s charge he sought to “make up” a reason for war.

“He’s claiming I misled America about weapons when he, himself, cited the very same intelligence about Saddam weapons programs as the reason he voted to go to war,” Bush said. Citing a lengthy Kerry quote from two years ago on the menace Saddam could pose, Bush said: “Just who’s the one trying to mislead the American people?”