WASHINGTON (AP) -- The White House urged Iraqi military commanders Monday to defy Saddam Hussein if he orders biological or chemical attacks on U.S. forces. President Bush planned to issue a similar warning in a Monday night speech designed to lay out his case against Saddam.

"The message to Iraqi commanders is, 'Think before you act'!" White House spokesman Ari Fleischer said. "You do not have to obey the orders Saddam Hussein gives you and the United States takes very seriously the criminal nature of these acts, particularly acts that would involve the use of chemical and biological weapons."

A year after he ordered the first military strikes in Afghanistan, Bush is offering what aides call his most comprehensive case yet on the threat posed by Iraq, and why a U.S.-led war on Saddam Hussein's regime may be necessary.

Monday night's speech in Cincinnati comes as Congress prepares to vote on resolutions authorizing force against Iraq. A vote in the Republican-controlled House, which has largely embraced the strong resolution he seeks, is expected Wednesday or Thursday; a vote in the Democratic-led Senate, where Bush has encountered more resistance, should come by next week.

Hours before the address, Sen. John Edwards, D-N.C., an early and strong proponent of strong action against Saddam, was accusing the Bush administration of "gratuitous unilateralism" that could undermine the war against terrorism.

"In word and deed," the administration "frequently sends the message that others don't matter," the potential 2004 Democratic presidential candidate said in the draft text of a speech he was to deliver to the Center for Strategic and International Studies.

"It rightly demands that our allies back efforts vital to America's interests, but then shows disdain for cooperative endeavors and agreements important to theirs," Edwards said.

Bush is trying to win over Americans and thereby pressure lawmakers and the United Nations, which is considering an Iraq resolution of its own.

Advisers compared the speech's style to Bush's August 2001 address in which he explained why he would allow limited federal funding for controversial research using stem cells derived from human embryos. In that address, he listed concerns raised by critics and answered them one by one.

The Iraq speech, scheduled for about 20 minutes, will break little, if any, new policy ground, Bush aides said. The speech will try to answer Americans' questions about potential war against Iraq, and counter critics' doubts about the imminence of the Iraqi threat, the aides said.

"He will frame the debate in a new and different way than he has in the past," White House communications director Dan Bartlett said.

Other officials would not rule out Bush discussing new facts or intelligence about the threat posed by Iraq, but they said that was not the purpose of the address.

One senior official, speaking on condition of anonymity, said the administration believes the public is behind the president on Iraq, an assertion borne out by a CBS-New York Times poll released Sunday.

Two-thirds of respondents favored use of the military to remove Saddam. But the figure dropped sharply when those surveyed were asked about the prospects of substantial U.S. losses, significant Iraqi civilian losses and prolonged combat.

The biggest question Bush intends to answer is why he believes immediate disarmament by Iraq is necessary, a second senior official said.

Bush has been sharpening his rhetoric, and shifting his arguments slightly, in the run-up to the speech, which he polished between weekend fund-raising appearances in New England.

While the long-standing American policy is "regime change" in Baghdad, Bush in recent speeches has avoided mentioning Saddam's ouster, emphasizing instead the urgency of "disarming" Iraq.

He went out of his way to cast war as a last resort, and as an undertaking that would only come with allies standing alongside U.S. troops.

Yet, for the first time, he called Saddam a "cold-blooded killer" -- a phrase usually reserved for Osama bin Laden and his al-Qaida cohorts.

And Bush warned in stark terms of the danger of letting Saddam continue to flout U.N. resolutions demanding he disarm. "Delay, indecision, and inaction are not options for America, because they could lead to massive and sudden horror," he said.

Bush offered no U.S. intelligence data to support his fears, and aides said he may not offer any new details in Monday's address. The purpose of the address, they said, was to synthesize the case against Saddam with blunt rhetoric and assure Americans that administration plans are well thought-out.