Declaring that "a line has been drawn in the sand," President Bush announced yesterday a major deployment of U.S. military forces in Saudi Arabia to take up "defensive positions" to protect against possible attack from Iraqi troops massed on the border with Kuwait.

Bush equated the commitment to defend Saudi Arabia and other Arab nations in the Persian Gulf to the four-decade "struggle for freedom in Europe," and compared Iraqi President Saddam Hussein to Adolf Hitler. "If history teaches us anything, it is that we must resist aggression or it will destroy our freedoms," Bush said in a nationally televised speech from the Oval Office yesterday morning.

Although Bush said the United States is not preparing for "a long ground war" in the Persian Gulf region, he nonetheless warned Americans to be prepared for a lengthy commitment. Saying that "standing up for our principles will not come easy," the president said, "It may take time and possibly cost a great deal."

As Bush spoke, the first wave of U.S. warplanes and combat troops began arriving in Saudi Arabia, while military leaders continued preparations for sending additional ground and air forces in coming weeks. The deployment, the largest since the Vietnam War, could exceed 50,000 troops and hundreds of fighter jets and bombers within the next month, according to Pentagon officials.

Saying "we're not in a war," Bush emphasized that the deployment of forces was intended for defensive reasons, not to push Saddam's troops out of Kuwait, which was overrun last Thursday in what Bush called "blitzkrieg fashion." Bush said he hoped that the economic sanctions ordered on Monday by the United Nations Security Council would squeeze Iraq sufficiently to induce its withdrawal from Kuwait.

"My military objective is to see Saudi Arabia defended," he said. "Our overall objective is to see Saddam Hussein get out and go back and to have the rightful regime of Kuwait back in place."

Bush said the U.S. forces would work with Saudi Arabia's 65,000-man ground forces and other nations to deter the estimated 200,000 Iraqi troops now threatening Saudi Arabia in southern Iraq and along the Kuwaiti border. Britain was the first to announce that it would offer air support. Pentagon officials said they believed other countries, including Arab nations, would contribute ground forces, but none publicly stepped forward yesterday to do so.

Secretary of State James A. Baker III, en route to Turkey, said yesterday that the United States is increasing contacts with Syria and Iran, two enemies of Iraq, in the effort to pressure Saddam, Washington Post staff writer David Hoffman reported.

Bush's risky decision to commit U.S. forces to possible action in the Middle East, which came after days of intensive negotiations and consultations with world leaders, drew strong bipartisan support on Capitol Hill, as members of Congress rallied behind an action they called a prudent and necessary response to a clear threat to America's economic interests.

"Democrats and Republicans, House and Senate . . . are very strongly of the opinion the president had to act, and if he waited, if he allowed the seizure of Kuwait to become not only a fact but to intimidate other countries in the gulf region, we might have a situation that would truly be irreversible," House Speaker Thomas S. Foley (D-Wash.) said.

But in his speech and in a later news conference at the White House, Bush made clear that the United States was prepared to protect "the freedom and independence of all those countries" in the gulf who might now feel threatened by Saddam's aggression.

"No one, friend or foe, should doubt our desire for peace," he said, "and no one should underestimate our determination to confront aggression."

Although Bush said his commitment of troops was not "open-ended," Defense Secretary Richard B. Cheney told reporters it is impossible to predict how long U.S. forces will be required to remain in the gulf region.

At a Pentagon news conference, Cheney said that to "put forces of significant size" into Saudi Arabia "is a new departure for us. The situation is uncertain. We don't know how long it will last; we don't know when it will end."

Bush said U.S. forces were invited into Saudi Arabia by King Fahd, who had several telephone conversations with Bush about the crisis and who met with Cheney and other U.S. officials on Monday. "The sovereign independence of Saudi Arabia is of vital interest to the United States," Bush said.

Bush also made clear that disruption of Saudi oil supplies would represent a "major threat" to U.S. "economic independence."

Pentagon officials said two squadrons totaling 48 Air Force F-15 fighters, as well as five airborne warning and control aircraft (AWACS) and the 2,300-man division ready brigade of the 82nd Airborne Division, were reaching Saudi bases yesterday. In addition, two heavily armed U.S. aircraft carrier battle groups moved into position on either side of the Arabian peninsula.

The first military forces left the United States at 7:35 a.m. Tuesday, more than 24 hours before Bush publicly announced his plans to deploy troops to the region. A senior administration official said the delay in announcing the deployment resulted from a desire to let the Saudis make a statement at the time of arrival and to head off any Iraqi advance into Saudi Arabia.

Joint Chiefs of Staff Chairman Colin L. Powell said that even if Iraqi forces cross the border before all American troops and aircraft are in place, U.S. warplanes based on the carrier USS Independence in the Gulf of Oman and the USS Dwight D. Eisenhower in the Red Sea could repel the attack.

"They are not invincible and they're not ten feet tall," Powell said. "And we have capabilities that we are now bringing to bear to insure that we, in concert with the armed forces of the Kingdom of Saudi Arabia, can deal with the threat."

Because Saddam has used chemical arms before, U.S. officials expressed concern about that possibility if a conflict begins. Powell said that while intelligence reports suggesting Iraq was moving chemical weapons are "somewhat ambiguous," chemical warfare is "a threat we're concerned with, and I treat it as a capability that is there and could be used."

Powell said U.S. forces deployed to the region have been equipped with masks and clothing to protect them from chemical contamination, as well as medicines that could serve as antidotes to the chemicals.

U.S. military planners also are prepared to send a tank brigade from the 24th (Mechanized) Infantry Division at Fort Stewart, Ga.; a brigade from the 101st Airborne Division at Fort Campbell, Ky.; the 7th Marine Amphibious Brigade at 29 Palms, Calif.; and the 1st Marine Amphibious Brigade based in Okinawa. In all, the deployment could exceed 50,000 ground troops.

Military officials said the deployment of heavy equipment and large numbers of troops, many of whom will be moved by ships, would take about a month. Although Powell and Cheney refused to discuss future deployments, military authorities said the extra troops and equipment will be sent over a period of weeks.

The administration has signed a waiver on the number of U.S.-built F-15 fighter planes allowed in Saudi Arabia. A 1988 amendment to the defense authorization bill, offered by Sen. Howard M. Metzenbaum (D-Ohio), limited the number to 60. A Metzenbaum spokeswoman said that the senator sought the limit because at the time, Saudia Arabia "had no professed enemy in the region" and that additional F-15s would serve only to threaten Israel.

Bush said his policy was guided by four objectives: withdrawal of Iraqi troops from Kuwait; restoration of the Kuwaiti government; U.S. security in the region, and protection of American lives.

Saying the 1930s taught the world that "appeasement does not work," Bush said that because Saddam's promises "mean nothing," the United States "must recognize that Iraq may not stop using force to advance its ambitions . . . . To assume that Iraq will not attack again would be unwise and unrealistic."

U.S. intelligence officials reported no major additions to the Iraqi forces in Kuwait but said Saddam's troops there have been fully resupplied and reinforced and "could move south in a couple of hours' notice."

Members of Congress, who were briefed yesterday afternoon on the developments, were unanimous in support of Bush's actions.

Senate Majority Leader George J. Mitchell (D-Maine), calling the invasion of Kuwait "an outrageous act of aggression," said all Americans would support the president's decision to deploy troops.

"He's doing precisely the right thing," said Senate Minority Leader Robert J. Dole (R-Kan.). "He's drawing more than a line in the sand, he's insisting the line go back" by demanding that Iraq withdraw from Kuwait.

House Armed Services Committee Chairman Les Aspin (D-Wis.) said, "This is much more important than {previous U.S. military actions in} Panama, Libya or Grenada. What we are talking about is our economic well-being."

Rep. Lee H. Hamilton (D-Ind.), while offering strong support for Bush, said he should have put more emphasis in his morning speech on what diplomatic efforts he will make to get Iraq out of Kuwait.

House Foreign Affairs Committee Chairman Dante B. Fascell (D-Fla.) expressed some concern that other nations contribute ground forces to the defense of Saudi Arabia. "I would hope that in the assignment of difficulties that it would not be a multinational force simply on the sea and in the air," he said.

Staff writers Charles R. Babcock, Ann Devroy, Tom Kenworthy and George C. Wilson contributed to this report.

ARMY

The 2,300-man division ready brigade of the 82nd Airborne Division arrived in Saudi Arabia yesterday.

AIR FORCE

1. Two squadrons of F-15Cs and Ds left Langley Air Force Base, Va., Tuesday night. The first planes arrived in Saudi Arabia yesterday.

2. Five U.S. AWACS, supplementing those already operated by Saudi forces, arrived in Saudi Arabia yesterday with aerial refueling tankers.

NAVY

3. Joint Task Force Middle East, prepositioned in the Persian Gulf, consists of seven ships and the command vessel USS La Salle.

4. USS Independence battle group has taken up position in the Gulf of Oman. It prepared for operations Tuesday.

5. USS Eisenhower battle group has taken up position in the Red Sea with the USS Scott and the Aegis guided-missile cruiser USS Ticonderoga.