WASHINGTON (CNN) -- Democratic presidential candidate Sen. Joe Biden on Tuesday said he can't believe President Bush hasn't known for months about a recent intelligence estimate that downplays the nuclear threat from Iran.
Other Democratic candidates also slammed Bush for continuing to ratchet up the rhetoric against Tehran.
On Tuesday the president acknowledged he had given a speech warning that Iran's nuclear development risked "World War III" about two months after his intelligence chief told him a reassessment of Tehran's nuclear ambitions was under way.
Bush told reporters during a White House news conference that he was not told the details of the new assessment until last week and he said the new report, which found that Iran had halted its nuclear weapons work in 2003, will not change U.S. policy toward Iran.
"Iran was dangerous, Iran is dangerous and Iran will be dangerous if they have the knowledge necessary to make a nuclear weapon," Bush said, pointing out that Tehran continues to try to enrich uranium for civilian purposes and therefore develop technology that could be used for a weapon.
"They had the program. They halted the program. It's a warning signal because they could restart it," he said. Watch Bush's credibility questioned »
Bush told reporters that he was told of "new information" about Iran in August during a briefing by Adm. Mike McConnell, the director of national intelligence.
"He didn't tell me what the information was. He did tell me it was going to take a while to analyze," the president said. He said he wasn't briefed about the new information until the new intelligence report was prepared last week.
The Democratic presidential candidates were incredulous that Bush did not know about the assessment's new finding.
Biden, the chairman of the Senate Foreign Relations Committee, called that explanation "unbelievable."
"Are you telling me a president that's briefed every single morning, who's fixated on Iran, is not told back in August that the tentative conclusion of 16 intelligence agencies in the U.S. government said they had abandoned their effort for a nuclear weapon in '03?" Biden asked in a conference call with reporters.
"I refuse to believe that," he added. "If that's true, he has the most incompetent staff in modern American history, and he's one of the most incompetent presidents in modern American history."
The Bush administration has spent years warning that Iran's development of nuclear power plants and enriched uranium masked an effort to produce an atomic bomb. Top officials have called the prospect of a nuclear-armed Iran "unacceptable."
In an October 17 news conference, Bush said that "If you're interested in avoiding World War III, it seems like you ought to be interested in preventing them from having the knowledge necessary to make a nuclear weapon."
And four days later, Vice President Dick Cheney told a Washington think tank that Iran would face "serious consequences" from the international community if it continued to enrich uranium.
But in a report released Monday, U.S. intelligence agencies concluded that Iran had suspended nuclear weapons work in 2003 and was unlikely to produce enough weapons-grade uranium for a bomb until at least 2010.
The assessment reverses a 2005 National Intelligence Estimate that found the Islamic republic was "determined to develop nuclear weapons despite its international obligations and international pressure." See how the 2005 and 2007 estimates differ »
The United States and its European allies are pushing for tighter sanctions against Tehran as a result of that continued refusal, and Bush said Monday's report "makes it clear that the strategy we have used in the past is effective."
But Biden said Monday's report was an unpleasant echo of the run-up to the U.S. invasion of Iraq in 2003 -- a war that was launched based on mistaken conclusions about Iraq's weapons programs. He said the result of Bush's rhetoric has been to make it "far more difficult" to round up support for continued sanctions on Tehran.
"It's hard to think of a more serious and more self-inflicted wound to our national security than this president continues to inflict," Biden said.
Republican National Committee spokesman Brian Walton accused Biden of trying to bolster his own presidential campaign.
"Apparently Joe Biden has seen recent polling that shows his statistical insignificance and is looking for relevance in the debate by offering heated rhetoric," Walton said.
Biden and other Democrats now hoping to replace Bush after 2008 used the report to call for new talks with Iran over the nuclear issue, offering the prospect of renewed economic and diplomatic ties in exchange for a halt to uranium enrichment.
"I think we do know that pressure on Iran does have an effect," Sen. Hillary Rodham Clinton, D-New York, said during a Democratic debate Tuesday held by National Public Radio. "I think that is an important lesson. But we're not going to reach the kind of resolution that we should seek unless we put that into the context of a diplomatic process."
And Sen. Barack Obama, D-Illinois, told the same forum that Bush "continues to not let facts get in the way of his ideology."
"They should have stopped the saber rattling; should have never started it. And they need, now, to aggressively move on the diplomatic front," he said.
But national security adviser Stephen Hadley said Monday that Bush was not told to tone down his rhetoric about Iran's nuclear ambitions when advised that a change in the U.S. estimate was coming -- and would have made his remarks about "World War III" either way.
"It was making a point that the president and we have been making for two or three years -- that the international community has to exert more pressure, because Iran needs to suspend [its] enrichment program," Hadley said. "That continues to be our policy after this latest National Intelligence Estimate."
And Bush said the new estimate "doesn't do anything to change my opinion about the danger Iran poses to the world -- quite the contrary." E-mail to a friend