WASHINGTON — The White House said Thursday that President Bush has evidence that Iraq retains hidden caches of weapons of mass destruction, dramatically raising the stakes in the U.S. confrontation with Saddam Hussein and suggesting that Bush is preparing for war. Top aides to Saddam have said Iraq will report to the United Nations this weekend that Iraq is free of the chemical, biological and nuclear weapons and missiles that it was barred from possessing after the 1991 Persian Gulf War.
But White House spokesman Ari Fleischer said Bush had a "solid basis" for U.S. claims that Saddam is hiding such arms from U.N. weapons inspectors, who have generally reported cooperation from Iraqi officials in the early stages of their work.
"The Iraqi government has proved time and time again to deceive, to mislead and to lie," Fleischer said.
He did not offer evidence for the assertion that Iraq is misleading the inspectors.
But a senior U.S. official said this week that, once Iraq makes a report that the Bush administration expects to be false, the United States will push for more aggressive U.N. weapons inspections designed to prove its case. That effort will be backed by more American intelligence-sharing with the U.N. inspections teams, this official and others said.
First, U.S. experts plan to take several days or more to pore over what is expected to be a voluminous Iraqi report, looking for misstatements.
If the United States concludes that Iraq is failing to comply with a U.N. disarmament resolution that passed last month, it could ask the U.N. Security Council to approve military action against Iraq or, alternately, move on its own to topple Saddam.
Senior defense officials, speaking on condition of anonymity, said that the United States could start an air campaign against Iraq even though an invasion force has not yet been sent from the United States. The ground force could be dispatched as the air strikes progressed, they said.
Armor, ammunition and other hardware has been constantly moving to the region, said one senior defense official. "People are easy to move," the official said.
Such an approach would be a major departure from the U.S. strategy in the war that ended the Iraqi occupation of Kuwait in 1991. In Operation Desert Storm, the U.S.-led military coalition launched its opening air campaign only once it had built up a 500,000-strong ground force in Saudi Arabia.
The defense officials said that a continual buildup of some 10,000 troops, armor and other equipment in Kuwait has created a strong enough U.S. force to protect the country against Iraqi retaliation for an air campaign.
A second senior defense official said U.S. air forces would be greatly strengthened in mid-December, when there would be at least four aircraft carriers in position to launch strikes against Iraq.
The Bush administration's plan for now is to let the inspections continue while ratcheting up the military pressure.
A British intelligence dossier made public in September said Iraq already was preparing to conceal evidence from renewed inspections.
Iraq was continuing to produce chemical and biological weapons, had developed mobile laboratories for germ weapons production and was trying to acquire technology for making nuclear weapons, said the report, which was released by the government of Prime Minister Tony Blair, a key Bush ally. The CIA has reported similar conclusions.
The senior administration official said the U.S. government had more recent evidence that Iraq had attempted to deceive and manipulate the inspectors since the inspections resumed Nov. 27.
"They're moving stuff around. They're hiding it," said the official, speaking on condition of anonymity. "This is a little like spring training," with the Iraqis scouting the inspectors and figuring out how they will do their job, in order to mislead them, he said.
A U.S. intelligence official, asked about the claim, confirmed some evidence of what officials believe to be Iraqi noncooperation, although he suggested it was not a major transgression.
"I wouldn't steer you away from the notion that there may be some indications that they're not being entirely cooperative," said the official, who also requested anonymity.
A defense official, speaking on condition of anonymity, said "the Iraqi denial and deception of the past continues." He said the United States had detected Iraqi efforts to hide parts of their illicit weapons programs.
None of these officials would be more specific, citing the sensitivity of intelligence data.
A White House spokesman, also speaking on condition of anonymity, cited what he called two troubling incidents so far. In one, inspectors discovered that missile-related equipment that had been tagged by a previous inspection team was missing. In another, the Iraqis led inspectors to an artillery shell filled with poisonous mustard gas.
In the latter incident, however, Iraq already had divulged the existence of the artillery shell. Previous inspection teams had not destroyed it.
Iraq is required under the U.N. resolution to report by Sunday on what weapons of mass destruction it possesses.
A series of similar declarations that Iraq made throughout the 1990s were proved to be filled with misstatements and omissions.
Top aides to Saddam, including Deputy Prime Minister Tariq Aziz, said this week that Iraq would declare itself free of such weapons, but would acknowledge having materials that are "dual use" for military or civilian purposes. The same technologies used in making germ weapons are common in veterinary research, for example.
Former weapons inspector David Albright said the Iraqi leader appeared to have concluded that a new war with the United States was inescapable and there was no point in declaring the location of his weapons stocks.
"The resolution was a chance for Saddam to come clean," Albright said. "I think Saddam has concluded that war's inevitable."
Top U.S. officials said Bush planned to escalate the pressure on Saddam after Sunday's declaration by quickening the pace of military deployments to the Persian Gulf.
U.S. envoys have been telling allies of the United States that Bush is likely to go to war and asking for their support, said administration officials, who requested anonymity.
Deputy Defense Secretary Paul Wolfowitz recently visited key ally Turkey and NATO headquarters in Brussels, Belgium, while Deputy Secretary of State Richard Armitage is undertaking a similar mission to Asia.
The White House is sending other top officials across the globe in coming days, including Deputy National Security Adviser Stephen Hadley, Undersecretary of Defense Douglas Feith and Undersecretaries of State Marc Grossman and John Bolton.
It remains unclear when Bush will take public his case that Iraq is still hiding weapons of mass destruction. U.S. officials have said they want to document an extensive pattern of violations by Saddam.
The U.N. inspection team, known as the U.N. Monitoring, Verification and Inspection Commission, is required to present its own report to the Security Council in late January.
Bush's top national security advisers, who met Thursday to discuss the U.S. response to an Iraqi weapons declaration they expect to be false, are divided over what approach Washington should pursue.
Vice President Dick Cheney and Defense Secretary Donald H. Rumsfeld have led one group of officials in arguing that the United States is authorized to use military force based on nothing more than an untruthful declaration, according to U.S. officials and private analysts close to the administration. But Cheney and Rumsfeld appear to have lost that argument for now, officials said.
Secretary of State Colin Powell has resisted their arguments and stresses the need for international backing.
France and Britain interpret the U.N. resolution to say that Iraq faces "serious consequences" if it both provides a false declaration and impedes the inspectors' work.
After the resolution was approved last month, France checked with other Security Council members -- including the United States -- to confirm that they share this reading, a French diplomat said, speaking on condition of anonymity.
Diego Ibarguen contributed to this article.