BALTIMORE, AUG. 20 -- The United States crossed a threshold in the escalating crisis in the Middle East today when President Bush for the first time described Americans and other foreign nationals trapped in Iraq and Kuwait as "hostages" and demanded their immediate release.

Bush's characterization marked an abrupt reversal of the administration's policy not to call the detained Americans "hostages." It came after Iraqi President Saddam Hussein said that Americans and other foreign nationals would be kept as a shield against possible U.S. attack and set demands for their release.

"We've been reluctant to use the word 'hostage,' " Bush said in a speech to the Veterans of Foreign Wars annual convention here after he and a handful of key advisers decided Sunday night to change the administration's description of the detained Americans. "But when Saddam Hussein specifically offers to trade the freedom of those citizens of many nations he holds against their will in return for concessions, there can be little doubt that whatever these innocent people are called, they are, in fact, hostages."

Pounding the lectern, he then warned that he would hold the Iraqi government responsible for the safety of those held.

Bush also continued to invoke the specter of Adolf Hitler and the lessons of World War II as he renewed his harsh, personal attacks against Saddam. In a speech to a Republican fund-raiser in North Kingstown, R.I., later today, he called the Iraqi leader "a person whose values -- who has no values -- when it comes to respecting international law, a man of evil standing against human life itself."

In his remarks today both to the veterans and at the GOP fund-raising event in Rhode Island, the president offered a bleak picture of the unfolding crisis in the Persian Gulf region, warning that "right now it could get fairly tough over there."

Calling on Americans to prepare to make "personal sacrifice," he declared that the nation and its allies had embarked on a noble effort "to protect our world from fundamental evil."

In Washington, the State Department announced that 12 Americans were part of a group of foreign nationals taken by Iraqis over the weekend from three hotels in Kuwait City to an undisclosed location. A senior U.S. official said he believes the 12 were to be taken to Baghdad, where Iraqi authorities were believed to be holding 35 other Americans at undisclosed sites. The 12 Americans were rounded up with a group that the British Foreign Office said included 82 British citizens, bringing to 123 the number of Britons taken by the Iraqi soldiers in Kuwait.

State Department deputy spokesman Richard A. Boucher said he was unable to describe the circumstances under which the Americans left their hotels. Last week he had said that U.S. officials were advising Americans to remain in their homes but not to resist if directed to leave by the Iraqis.

The initial group of Americans and Britons taken by the Iraqis and held in Baghdad were among the 367 passengers on an India-bound British Airways jet that was stranded in Kuwait when the Iraqi invasion began.

A spokesman for British Airways in New York said some of the newly seized British citizens may have been among the remaining 295 passengers whom the airline said it had located at three hotels in Kuwait. "The last time we heard from them was on Friday. It appears some of them were split up and moved over the weekend," said spokesman John Lampl.

Boucher declined yesterday to comment on a broadcast by CBS News that an additional 35 Americans had taken refuge at the U.S. Embassy in Baghdad.

The State Department announced separately that it was advising all Americans not to travel to Jordan, citing the Iraqi invasion of Kuwait and "continuing unstable conditions in the region." An official noted that the action followed a warning Sunday that Americans should not travel to Yemen because of "anti-American demonstrations" there, but said the warning about Jordan was not the result of "any specific threat" against Americans.

Amid these diplomatic developments, a senior Army general said that by next week, when two brigades from the 24th Mechanized Infantry Division arrive in Saudi Arabia, the Army will have about 40,000 soldiers on the ground there. Other Army sources said there is concern that the forces now deployed in Saudi Arabia face a "window of vulnerability" until that division arrives with its contingent of tanks and other "heavy" fighting equipment. Most of the forces now in place are "light," and not well-equipped to combat a major armored attack by Iraq.

The Army also has moved "modest amounts of stuff" from Europe to the Persian Gulf, including helicopters and assorted supplies, Pentagon sources said.

Twenty F-117A "stealth" fighter planes that are designed to elude enemy radar left Langley Air Force Base for Saudi Arabia today. The squadron from the 37th Tactical Fighter Wing flew from the unit's home base in Nevada on Sunday; the remaining 36 F-117As remained in Nevada, according to Air Force Captain Susan Strednanski.

Before Bush's speech to the veterans today, the administration had assiduously avoided using the word "hostages" in an effort not to raise the value to their captors of the 3,000 Americans who have been trapped -- most in Kuwait but several hundred also in Iraq -- since the invasion and to avoid inflaming public opinion in the United States.

Administration officials hoped their low-key approach might help bring about the release of the Americans and avoid making them bargaining chips in the larger gulf crisis.

The hostage question and Bush's speech were among a number of issues discussed Sunday night during a two-hour dinner meeting at the White House between Bush and some of his national security advisers. According to administration officials, Bush was unhappy with the draft of the speech and wanted to toughen the language to reflect the weekend's developments in the Persian Gulf.

Saddam's new demands that U.S. troops leave Saudi Arabia and that the trade embargo against Iraq be lifted in return for release of the foreign nationals persuaded administration officials that they had no choice but to bow to reality and acknowledge that the Americans were now held hostage.

The final decision to describe the detained Americans as hostages came during an early morning meeting in the Oval Office today attended by Bush, White House Chief of Staff John H. Sununu, national security adviser Brent Scowcoft and others, officials said. The hostage language was drafted by this group and was then hastily inserted into the text of the speech.

The change in policy came quickly and apparently caught some administration officials by surprise. On Sunday afternoon, en route back to Washington, White House press secretary Marlin Fitzwater said in answer to a question that U.N. Ambassador Thomas Pickering had misspoken by calling the detained Americans hostages. "We would not use that word," Fitzwater said.

Today, Bush told reporters aboard Air Force One that his decision to use the word "hostages" was not aimed at "turning up the heat" on the Iraqis. Instead, he called the language "a semantical thing," saying the "situation is about the same as it was a few days ago."

"There's a recognition of the fact that now demands are being made for the release of people, and that, I think, is the definition of hostages," Bush said. He added that after discussing the issue this morning, he decided "why not just say that" they were hostages.

In his speech today, Bush called the detention of innocent civilians an "offense against all norms of international behavior," and added that "leaders who use citizens as pawns deserve -- and will receive -- the scorn and condemnation of the entire world."

The president called on Saddam to "release all foreigners now" and allow them "to come and go as they wish." He also accused the Iraqi leaders of violating the norms of their Moslem religion and Arab culture by holding foreign nationals against their will, rather than displaying traditional Arab hospitality to visitors.

Bush warned Americans that the commitment to deploy tens of thousands of troops to Saudi Arabia and the gulf region would mean "personal sacrifice" in the days and months ahead. He said "the outcome is not yet decided," and there are "hard choices" ahead.

"It was not with passionate haste, but really with a heavy heart, that I had to commit our troops to Saudi Arabia," Bush said. "I took this action not out of some national hunger for conflict, but out of the moral responsibility, shared by so many committed nations, to protect our world from fundamental evil." He added that peace was more than simply the absence of war and that "its preservation exacts an obligation."

The president repeatedly lauded other nations that have joined the United States to resist the "ruthless" Iraqi aggression against Kuwait, voicing special praise for British Prime Minister Margaret Thatcher as someone who "stands tall" for freedom. Bush talked with Thatcher before leaving Washington and also spoke by phone with Turkish President Turgut Ozal. Later he spoke with French President Francois Mitterrand for 30 minutes.

Bush's speech to the VFW audience was replete with references to American military battles from wars past, as he invoked the Normandy invasion, Pork Chop Hill, Khe Sanh and others. He was interrupted by applause more than two dozen times by the audience of several thousand veterans.Staff writers Rick Atkinson, David Hoffman and Bill McAllister in Washington contributed to this report.