An official said the plotters had completed preparations for their attacks, and all that remained to put the plot in motion "was to set the zero hour."
It was one of the biggest roundups since Saudi leaders began cracking down on religious extremists four years ago after militants attacked foreigners and others involved in the country's oil industry seeking to topple the monarchy for its alliance with the U.S.
But while the monthslong police operation provided a high-profile victory for the royal family, the large number of people arrested highlighted the extremism threat in the world's leading oil exporter.
The Interior Ministry said the plotters were organized into seven cells and planned to stage suicide attacks on "public figures, oil facilities, refineries ... and military zones," including some outside the kingdom. It did not identify any of the targets.
The militants also planned to storm Saudi prisons to free jailed militants, the ministry's statement said.
"They had reached an advance stage of readiness, and what remained only was to set the zero hour for their attacks," the ministry's spokesman, Brig. Mansour al-Turki, told The Associated Press in a phone call. "They had the personnel, the money, the arms. Almost all the elements for terror attacks were complete except for setting the zero hour for the attacks."
The Saudi statement said some of the detainees had been "sent to other countries to study flying in preparation for using them to carry out terrorist attacks inside the kingdom."
Al-Turki said he didn't know whether the militants who trained as pilots planned to fly suicide missions like those in the Sept. 11 attack on the United States or whether they intended to strike oil targets in some other way with the aircraft.
"I have no information on what they were planning to do with the airplanes, but I assume, based on the possible use of airplanes in attacks, that they planned to fly the airplanes into specific targets," he said.
The militants were detained in successive waves, with one group confessing and leading security officials to another group as well as caches of weapons, al-Turki said. He told the privately owned Al-Arabiya television channel that some of those arrested were not Saudis.
The Interior Ministry said police seized large quantities of weapons and explosives and more than $5.3 million in currency during the sweep. State TV showed video of one cache dug up in the desert that included explosives, assault rifles, handguns and ammunition wrapped in plastic.
U.S. officials praised the sweep as a blow to international terrorism.
"Certainly anytime the Saudis or anyone else takes action against those involved in terrorism it's a good thing," State Department spokesman Tom Casey said. "It's something that makes the world safer and makes America safer."
Saudi Arabia's long alliance with the United States angers Saudi extremists who object to Western ways, such al-Qaida leader Osama bin Laden.
An austere strain of Islam known as Wahhabism is followed by the country's predominantly Sunni Muslim population, and militant groups have attracted recruits from Saudis with extremist leanings. Fifteen of the 19 airline hijackers in the Sept. 11 attack were from here.
Militants have struck at foreigners living in Saudi Arabia and the country's oil industry, which has more than 260 billion barrels of proven oil reserves, a quarter of the world's total. Bin Laden also has urged such attacks to hurt the flow of oil to the West.
In May 2004, attackers stormed the offices of a Houston-based oil company in the western Saudi oil hub of Yanbu. The fighting killed six Westerners, a Saudi and several militants. Several weeks later, al-Qaida-linked gunmen attacked oil company compounds in Khobar on the eastern coast, killing killed 22 people, including 19 foreigners. During the most recent attack, in February 2006, two explosives-laden vehicles tried to enter the Abqaiq oil complex, the world's largest oil processing facility, in eastern Saudi Arabia. But guards opened fire and the vehicles exploded without damaging the facility. The ruling family has pursued an aggressive campaign against militants the past four years, and its security forces have managed to kill or capture most of those on its list of most-wanted al-Qaida loyalists in the country. The Interior Ministry did not say whether any of the militants rounded up in the latest sweep were members of al-Qaida, referring to them only as a "deviant group" - Saudi Arabia's term for Islamic terrorist. The kingdom earmarked one-sixth of its $12 billion defense budget last year for protecting oil facilities and is considering creation of special military units devoted to guarding the industry, Nawaf Obaid, a petroleum adviser with close ties to the government, has said. Previous reports have said attack helicopters and F-15 jet fighters are in the air 24 hours a day over Saudi oil export terminals, while as many as 30,000 soldiers guard oil facilities. (AP) Associated Press writers Abdullah Shihri reported from Riyadh, Saudi Arabia, and Donna Abu-Nasr from Beirut, Lebanon. AP-CS-04-27-07 1732EDT