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 months-long 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."
CBS News correspondent Richard Roth says the Saudi government did not reveal when the arrests occurred or when the weapons were found. But with almost a quarter of the world's oil reserves in Saudi Arabia, the news was enough to make markets edgy and nudge prices up.
On Wall Street, prices for light, sweet crude rose $1.40, to $66.46 per barrel. Nervous oil analysts said it could have been worse.
"You could have seen oil prices shoot $20, $30 a barrel," Phil Flynn of Alaron Trading said. "We could be talking, maybe, $100 a barrel oil if this were successful. This is a very dangerous potential situation."
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.
"It would appear given the fact that they were well-financed, that they had aviation skills — also explosive skills — that they were going to carry out some massive type of operation," Dr. Neil Livingstone, chief executive officer of the Washington-based security company Executive Action, told CBS News.
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.
Saudi television today showed a terrorist arsenal: A stockpile of explosives, dug out of the desert, along with handguns and rifles wrapped in plastic. Even more: Hidden under tile flooring and stuffed into drain pipes were stacks of Saudi cash, more than five million dollars' worth.
"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 Qaeda 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 Qaeda-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 Saudis said the men behind that attempted attack were among those arrested.
But the kingdom's oil fields remain a prime al Qaeda target — and despite repeated police raids and billions spent on security, the government knows they are still at risk.
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 Qaeda 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 Qaeda, 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.