RIYADH, Saudi Arabia — The death toll rose on Tuesday to 30, including at least eight Americans, and dozens were injured in a night of multiple terrorist truck bombings that targeted the large Western presence in Saudi Arabia and the Saudi monarchy itself.

As new details emerged of Saudi Arabia's deadliest terrorist attack in decades, it became clear the plot was large and well coordinated. The plotters struck with precision timing at three guarded residential compounds using multiple vehicles and extensive surveillance of the facilities beforehand, U.S. diplomats and soldiers said.

The suicide bombers, believed to be Islamic fundamentalists linked to al-Qaida, chose targets designed to damage the U.S. presence in the kingdom and punish Saudis who work with foreigners.

The attacks also were a major new threat to the monarchy that rules the oil-rich kingdom. The monarchy, whose oil is a pillar of the U.S. economy, already has been beset by popular discontent. The leadership is aging and uncertain. Unemployment is steep, and average incomes have declined sharply.

While the bombing apparently was intended to weaken the Saudi regime, it could embolden the normally cautious princes to crack down harder on Muslim extremists after years of tolerating and even financing them.

In an unusual address to his nation, Crown Prince Abdullah declared the terrorist attacks un-Islamic. "The perpetrators are but a small group of deviants whose objective is to do harm to our society by doing damage to its security," he said.

Citing passages from the Quran which prohibit killing of innocents, Abdullah said: "We specifically warn anyone who tries to justify these crimes in the name of religion."

At the residential compound of Vinnell Corp., a U.S. firm, the attackers came in two vehicles, shooting guards in an armored personnel carrier, killing one. In less than a minute, they overwhelmed a guard station, where bullet holes still pocked the glass 17 hours later.

Apparently knowing where it was, they flipped a switch and opened the main gate. The larger of the vehicles, a Dodge Ram truck packed with an estimated 400 pounds of plastic explosive, sped several hundred yards to the bachelors' quarters and detonated, said a U.S. Army general serving in Saudi Arabia.

The explosion, at 11:25 p.m. Monday night local time, was positioned for maximum impact. It sheared away much of the four-story building, imploded the roofs of nearby buildings and decapitated a nearby palm tree.

Other vehicles, apparently driven by suicide bombers using the same tactics, exploded at two more Riyadh compounds housing Saudis and foreigners at 11:20 p.m. and 11:22 p.m., said the general, speaking on condition of anonymity.

"It was a sophisticated near-simultaneous attack," he said.

"These despicable acts were committed by killers whose only faith is hate," President Bush said in Indianapolis. "The United States will find the killers and they will learn the meaning of American justice."

Virtually all of the U.S. casualties were at Vinnell, where at least seven Americans and two Filipinos were killed, and many others injured.

The defense contractor, with 800 workers in Saudi Arabia, helps the U.S. military train the Saudi national guard. The death toll would have been much worse if 50 out of the 70 people living in the bachelors' quarters had not been away on a nighttime desert training exercise.

"It certainly has all the fingerprints of an al-Qaida operation," Secretary of State Colin Powell said after a 15-minute visit to the rubble-strewn compound. For security reasons, the compound was built well away from the center of Riyadh, a city of 4.5 million people.

"This is criminality, terrorism at its worst," said Powell, who inspected a 10-foot deep crater left by the explosion.

Just beyond the crater lay the crumpled and blackened frame of the Dodge Ram.

Al-Qaida and leader Osama bin Laden are motivated in part by opposition to the U.S. presence in Saudi Arabia, the birthplace of Islam. They also want to overthrow the Saudi monarchy as part of a plan to establish an Islamic state across the Middle East.

To reduce tensions, Defense Secretary Donald H. Rumsfeld announced recently that U.S. combat troops — stationed in Saudi Arabia since Iraq's 1990 invasion of Kuwait — would be removed.

There was no evidence the attacks were planned to coincide with Powell's arrival to discuss terrorism and Middle East peace with Saudi Crown Prince Abdullah, the kingdom's de facto leader.

In fact, the U.S. Embassy here and the Saudi government had issued increasingly urgent warnings this month of the possibility of a major terrorist attack.

Last week, Saudi authorities seized 700 pounds of explosives after a shoot-out with suspected terrorists, who escaped. They announced they were searching for 19 people, 17 of them Saudis.

A U.S. official who talked to Prince Nayef, the Saudi interior minister, said the Saudis were convinced from interrogations of 150 al-Qaida sympathizers arrested recently that the terrorist network was in the final stages of executing a major attack in the kingdom. It was to target not just Westerners but also senior members of the royal family in an attempt to decapitate the regime.

Few Saudis were surprised.

"Everybody was waiting for these ... to take place," said Mohsen al Awajy, a Riyadh attorney who served time in jail for demanding political reform. "I predict more and more," he said. "I'm very worried about the future. I'm very, very concerned."

Privately, one Saudi official compared the unrest in his country's middle class to the turmoil that helped topple the Shah of Iran in 1979.

Mohammed Saed Tayeb, a reform activist in the Western port city of Jeddah, said he worried that the government would respond with a crackdown that would do nothing to improve the country's situation.

He called for the monarchy to begin a dialogue with its opponents.

A senior administration official said "the regime, the government, the family remains stable, in charge," but is increasingly aware of the need for reforms.

The attacks stoked fears in Saudi Arabia's large expatriate community.

Two Saudi armored personnel carriers were moved into place by Tuesday morning outside the already heavily guarded U.S. Embassy.

A team of FBI agents was also sent to the scene.

Fairfax, Va.-based Vinnell has been working in Saudi Arabia for 29 years to help train the Saudi national guard. It is a subsidiary of Northrop Grumman Co., the defense contractor.

In 1996, a truck bombing at the Khobar Towers complex housing U.S. Air Force personnel killed 19 servicemen and injured hundreds of people.

In 1979, Islamic fundamentalists took over the Grand Mosque in Mecca, Islam's holiest site. Six hundred people were killed when the mosque was retaken after a two-week siege.

Some analysts say the departure of U.S. combat troops — the training mission will remain — and a more aggressive Saudi crackdown on Islamic extremists may be too little and too late to save the regime.

"The Pentagon decision to relocate most of the U.S. forces from the kingdom to Qatar, ostensibly because the threat from Saddam is gone, will help staunch some of the bad feeling for the Saudis," said former Pentagon official Noel Koch, now head of the consulting firm TranSecur, Inc.

But, Koch said, "Saudis who opposed their government in the past will still find plenty of reason to do so now. Many, like (those) who seized the mosque a quarter century ago, remain angry over widespread corruption among the royals, their cultural and political ties to the West, the excesses of the thousands of princes, and an economy that continues to deteriorate."