The United States and its allies went to war against Iraq last night as hundreds of warplanes unleashed a massive bombing attack against targets in Iraq and occupied Kuwait.

"Tonight the battle has been joined," President Bush said in a brief, nationally televised address at 9 p.m. "Our goal is not the conquest of Iraq, it is the liberation of Kuwait."

Wave after wave of warplanes attacked Baghdad, hitting oil refineries, the international airport and the presidential palace of President Saddam Hussein. Witnesses reported that the night sky was thick with tracer fire from antiaircraft guns and that a smoky pallor had settled over the Iraqi capital. Western correspondents reported that much of the city had been blacked out, although not until nearly an hour after the raids began.

The first targets hit, according to U.S. military sources in Saudi Arabia, were ground-to-ground Scud missiles capable of striking Saudi or Israeli cities. "Our planes went in. The bombs went down. There has been no reaction from the Iraqi side," said a Saudi spokesmanin Dhahran.

Bush said that the attacks also are intended to destroy Iraq's nuclear weapons potential and chemical weapons stocks, as well as damaging Saddam's tank force. "We will not fail," the president added.

The order to launch attacks marked the end of 5 1/2 months of diplomatic and economic efforts by the United Nations to force Iraq's Saddam Hussein to roll back the forces he sent into oil-rich Kuwait on Aug. 2.

"Some may ask," Bush said, "why not wait?" The reason, he said, is that "the world could wait no longer." Initial reaction from Capitol Hill showed bipartisan support for the president's decision. Congress had authorized military action in votes last Saturday.

Air raid sirens erupted at 7:19 p.m. (EST) in the city of Dhahran in eastern Saudi Arabia, and officials ordered civilians, many of whom donned gas masks, into shelters. Sirens also sounded in Riyadh, the Saudi capital, about 45 mintues later, although there were no reports of actual Iraqi attacks.

The allied attack, code named Operation Desert Storm, included extensive participation by 45 British Tornado jets flying out of Saudi Arabia and Bahrain, and 150 Saudi attack fighters, according to British and Saudi sources. Unconfirmed reports last night indicated that the first waves of allied planes had returned safely from their missions.

The beginning of the war, though not unexpected after the failure of all diplomatic efforts to force Iraq from Kuwait, nevertheless stunned the nation and the world, in part because it began less than 18 hours after the expiration of a United Nations ultimatum to Saddam. The attacks brought to a violent head a crisis that began with Iraq's swift invasion of Kuwait; Saddam had defied repeated U.N. demands that he pull his forces out.

U.S. military officials said that the air war against Iraq could last for three to four weeks before ground forces swing into action, although Bush may order brief pauses in the bombing to give Saddam an opportunity to sue for peace. The first phase of the air war targets Iraqi air defenses, command and control centers and Iraqi Scud missiles; it was not clear whether the attack on the Scuds -- capable of striking Israel -- was successful, although there was no indication that Israel had been hit or that Israeli forces were involved in the war.

Israeli Air Force Col. Menachem Eynan told a radio reporter two hours after the air strikes began that "we're completely out of the picture. We're not involved, and we're not acting."

One objective of the attack last night and in the coming days, Pentagon sources said, is to sever Iraqi forces in Kuwait from central government and military control in Baghdad. Subsequent phases of the air war will seek to isolate those forces logistically -- by demolishing roads, railroads and supply lines -- and then begin destroying the forces themselves.

Oil prices surged upward within minutes of the first reports of bombing. The formal oil market in New York was closed, but traders in Singapore and on the the informal worldwide market bid the price up more than $3, to nearly $35 a barrel.

After a meeting at the State Department yesterday morning, Secretary of State James A. Baker III called Saudi Ambassador Bandar bin Sultan to tell him of Bush's decision to begin the attack. Bandar then telephoned King Fahd in Saudi Arabia and notified him through use of a secret, pre-arranged code word, according to a source close to the Saudi government. The king then assented to the attack with another code word.

A military spokesman in central Saudi Arabia said the first squardron of F-15E fighter bombers took off at 4:50 p.m.(EST). Col. Roy Davies, chief maintenance officer at the base, said, "This is history in the making."

The first official notification of the attack came from a grim-looking White House press secretary Marlin Fitzwater, who appeared in the White House briefing room just after 7 p.m.

Reading a statement from Bush, he said, "The liberation of Kuwait has begun. In conjunction with the forces of our coalition partners, the United States has moved under the code name Operation Desert Storm to enforce the mandates of the United Nations Security Council. As of 7 p.m. Eastern Standard Time, Operation Desert Storm forces were engaging targets in Kuwait and Iraq."

Fitzwater said the attack is "designed to accomplish the goal of the U.N. Security Council resolution to get Iraq unconditionally out of Kuwait. I think the president's description of it a few days ago, that it would be swift and massive, would certainly apply."

As U.S. officials prepared to announce the attack, protesters in Lafayette Park across Pennsylvania Avenue from the White House stood in a light rain chanting obscenities. "One, two, three four, we don't want your {expletive} war," they said over and over again.

Bush was in the small study off of the Oval Office watching television reports from Baghdad as the attack began. With him were Vice President Quayle, national security adviser Brent Scowcroft and White House Chief of Staff John H. Sununu. Fitzwater was in and out of the office during that period.

As the sound of the bombing came over the television, Bush turned to his aides and said, "It's just the way it was scheduled," Fitzwater reported. He described the president as "very matter-of-fact and calm" as he watched the live reports from Baghdad.

Moments later he said to Fitzwater, "Marlin, you'd better go do it," the signal for the spokesman to give the official announcement.

Fitzwater said the decision was made over a period of weeks, with key meetings occurring on several recent Sunday nights after the president returned from Camp David. A final planning meeting came Tuesday morning at the White House. But the decision had been implicit from the start.

From the day of Iraq's invasion on Aug. 2, Bush had made it plain that he thought that the stakes in the gulf were big enough to justify a war. He persuaded 28 nations to send forces to the gulf and mobilized support from past adversaries, including the Soviet Union, for an embargo that largely isolated Iraq from world commerce.

With the backing of an unprecedented range of countries, the United Nations Security Council passed 12 separate and increasingly severe resolutions demanding that Iraq roll back its lightning conquest of the tiny desert kingdom and its rich oil reserves. Last Saturday, Bush obtained what amounted to a congressional declaration of war, when the Senate narrowly and the House by a wider margin approved a resolution endorsing the use of "all necessary means" for expelling Iraq -- the same formulation the United Nations had used in its last ultimatum to Saddam Hussein.

Although the United States had "tilted" to Iraq's side in the Iran-Iraq war and had sent diplomatic signals early last summer that it had no inclination to intervene in the long-simmering Iraqi territorial dispute with Kuwait, Bush insisted from the day of the invasion that Saddam military conquest of Kuwait "will not stand."

He never wavered from that view in the five months that led up to the most important decision of his presidency and as H-Hour approached seemed almost relieved that the waiting was over.

His only appearance during the day came at the beginning of a meeting with educators. When asked about his mood, he said, "Life goes on." When reporters commented that he looked grim, his response was to tell them to "lighten up."

Fitzwater described him early in the day as having "steeled himself" for the events ahead and as being "calm and confident" that he had taken the right course.

Reading from a prepared statement at that morning briefing, Fitzwater said, "The president has gone beyond the extra mile for peace. Saddam Hussein has yet to take the first step."

By early afternoon, the signs of an imminent military attack, familiar from the the Panama invasion a year ago, began emerging in rumor form on Capitol Hill. Unusual signs of activity were observed in the offices of House Speaker Thomas S. Foley (D-Wash.) and Senate Majority Leader George J. Mitchell (D-Maine).

Between 5 and 6 p.m., congressional leaders began getting calls from Bush and other administration officials, informing them that hostilities were under way. Sen. Robert C. Byrd (D-W.Va.) recalled telling the president, "My Bible tells me that Our Heavenly Father . . . will reward us. I pray for you every night."

By 6:35 p.m., the leaders had received the written certification, required by the congressional resolution, saying that all diplomatic efforts had failed.

Security, already tight, grew even stricter. Squads of Capitol police, clad in slate-gray jump suits and accompanied by guard dogs, moved around the building. Virtually every office in the White House was at work, but many officials had simply been warned not to go home without being given an explanation.

The FBI refused to comment on reports that its agents were preparing in the event of hostilities to conduct searches of locations where suspected terrorists might be hiding out and perhaps make some arrests.

"Anything that is being done is being done within the limitations of the law," FBI spokesman Carlos Fernandez said last night. He said he was not aware of any searches that might be underway. "If it is being done," he said, "it's something I wouldn't be able to talk about anyway.

Domestic airlines and airports were ordered at about 8 p.m. to go to a heightened state of security, according to government sources, although "no specific credible threat of terrorism has been received against any airline.

The government imposed what it called "preplanned security level 3", one step below the most stringent security requirements. Under level 3, more uniformed police are moved into airports and a more stringent "profile" is applied to passengers in determining who to question and search.

In addition, access to airports is tightened, and gate areas are limited to ticketed passengers only. More stringent searches, and long lines, are likely at security checkpoints.

Officials at the Pentagon, White House and State Department had been suggesting for almost a week that should Saddam fail to withdraw, force would be used and it would be "sooner rather than later." Secretary of State Baker, visiting with the troops in Saudi Arabia last Friday, told them their wait for action would be a short one.

A senior administration official who briefed reporters last week outlined the president's rationale for moving quickly. "If the 15th comes and goes and he {Saddam} stands there and has defied the United Nations . . . and gotten away with it," that would make him "a hero to the Arabs."

The official suggested a wait much beyond the deadline would split the fragile coalition of anti-Saddam nations. If the deadline passed without action, he said, Saddam could "claim he stood down the world" and perhaps retain an aura of "heroism" even if he then backed down.

Fitzwater said he knew that the attack was scheduled for tonight several days ago. The statement he read at 7 p.m. was written on Tuesday.

Asked about Bush's demeanor during the day, Fitzwater said, "He's been calm, expectant."

Fitzwater said Bush would receive continual updates on the fighting from Scowcroft in the White House Situation Room and from Cheney and Powell at the Pentagon.

Fitzwater said that aides who observed the president during the day could see "the gravity of the situation" in the president's face. He said that a White House photo of Bush and Baker, who lunched at the White House, showed "lines of concern in his face."

Asked whether the beginning of the attack, coming after a long and harrowing countdown to the midnight deadline Tuesday had broken the tension in the White House, Fitzwater said no.

"I don't think anybody anticipates that it's going to be easy," he said.

Fitzwater also said the president was particularly concerned about the presence of American journalists in Baghdad and that, beginning on Jan. 10, asked his spokesman to urge reporters to leave the Iraqi capital. When it was clear by yesterday morning that not all reporters were planning to leave, Bush asked Fitzwater to make another appeal.