WASHINGTON (AP) -- The State Department issued a new worldwide warning Tuesday night that Americans may be the target of terrorist attacks in the New Year period. Large groups of people, assembled for religious festivals or to mark the millennium, may be especially at risk, the department said.

Arrests in Jordan last week have produced information that hotels, tour buses and tourist sites in the Arab kingdom may have been targeted, the statement said. However, even after the arrests of 13 suspects, ``we cannot rule out the possibility that attacks still may be planned for this and other parts of the world,'' the department said.

Amid heightened concerns about the possibility of a holiday terrorist attack at home as well as abroad, security was ordered tightened Tuesday at American airports and the Pentagon said it was taking ``appropriate action'' to protect U.S. forces overseas.

White House spokesman Joe Lockhart reiterated a State Department warning that there was ``credible information'' about potential terrorist threats abroad, and that Americans should stay in touch with U.S. embassies or consulates. An earlier worldwide caution was issued Dec. 11. At the time, a senior U.S. official said, the U.S. government knew a plot had been uncovered in Jordan.

``The announcement was designed to keep Americans abreast of the counter-terrorism operation,'' said the official, who spoke to The Associated Press on condition of anonymity. The official also said authorities were looking for a 31-year-old U.S. citizen from California with ties to Osama bin Laden, the Saudi exile the Clinton administration considers the mastermind of a worldwide terrorist operation.

The new warning to Americans was stated clearly: ``The U.S. government believes that terrorists may be planning to conduct attacks, including against official and non-official Americans, in and around the New Year period, from now through mid-January 2000.''