The arrests were not based on hard evidence the people detained belonged to terrorist groups, including a network the U.S. government believes is headed by Osama bin Laden, the Saudi expatriate who was given sanctuary in Afghanistan, the officials said.
Unless questioning produces useful or incriminating information, they are likely to be released early next year, said the officials, speaking on condition of anonymity.
Apart from concern about potential terrorist attacks, the approaching end of the millennium has heightened anxieties, especially in the Middle East, the officials said.
Meanwhile, the head of the State Department's office to counter terrorism intends to celebrate New Year's Eve on the National Mall, despite warnings that Americans might be the target of possible attacks around the world.
"I am going there to enjoy myself," coordinator Michael A. Sheehan said Tuesday in an interview. "There are no guarantees in life."
A year into his job, Sheehan also said that the breakup of a suspected terrorist cell in Jordan has provided new leads in the drive against Osama bin Laden, the Saudi exile accused of masterminding attacks on two U.S. embassies in Africa last year.
"The bust was a really significant event," he said.
Interrogation of the suspects provided information clearly linking bin Laden with a planned attack in Jordan, he said, and it "told us we ought to be worried about other groups" that may be planning attacks in other countries.
Still, the level of suspicious activity has risen only slightly since the State Department issued worldwide warnings earlier this month, Sheehan said, though he said the alert stands.
Sheehan said he would wear a heavy coat and a warm hat to the mammoth New Year's Eve event at the Lincoln Memorial, where thousands, including President Clinton, will welcome in the New Year in a Hollywood-style entertainment extravaganza.
"I've read all the stuff coming in, and I intend to be there. If I see something suspicious, I'll report it to the first cop," Sheehan said.
The State Department's Dec. 11 warning, reaffirmed Dec. 21, told Americans planning to assemble for religious festivals or to mark the millennium they could be especially at risk. Security was tightened at airports and at the nation's borders.
Even so, the level of suspicious activity has risen only slightly, Sheehan said.
"People have questioned whether our warnings were hyped," he said in the interview in his office. "I don't think so."
Even with new security measures at the State Department visitors must be escorted, and officials who work in the building cannot go far without passinthe identity tags they wear around their necks through turnstiles the door to Sheehan's office was open when a reporter arrived for a scheduled interview.
"You could be hit by a bus," he said philosophically about his New Year's plans.
At the same time, Sheehan will drop by his office on the government holiday to check on developments around the world. He said he is especially vigilant over peace talks due to be held next week between Israel and Syria in Shepherdstown, W.Va.
"We are determined not to let any group disrupt the peace process," he said. "But as we make progress, there are groups determined to use violence to disrupt it."