The State Department said yesterday it is "seriously concerned" about the threat of terrorist attacks in the event of military conflict with Iraq and reiterated President Bush's warning that the United States will hold Iraqi President Saddam Hussein "directly responsible" for any such occurrences.

State Department spokesman Richard Boucher said there have been "repeated examples of planning for terrorist activity, including surveillance of potential American targets" since Iraq's invasion of Kuwait Aug. 2.

Boucher declined to elaborate, but a senior State Department official said later that U.S. diplomats abroad have reported noticing "suspicious people hanging around their apartments," evidently studying their homes, and cars with occupants using videotape cameras repeatedly driving past their embassies.

Apparently those conducting the surveillance are trying to determine when U.S. officials come and go, their routes to work, the cars they use and the precautions they take.

U.S. military installations have also reported signs of terrorist "casings" of their facilities, officials said.

One administration official said the "proliferation" of such activity since Iraq's invasion of Kuwait has been striking. U.S. diplomats and military officials have reported suspicious sightings throughout Europe, the Middle East and North Africa, he said.

Boucher told reporters at a regular briefing that "Iraqi officials and terrorists sponsored by Iraq have publicly threatened a terrorist campaign in the event of hostilities, and we take these threats seriously.

"I recall for you the words of President Bush on Sept. 21," Boucher added. "He said: 'Terrorism concerns me, it will continue to concern me, and I will hold him -- Saddam Hussein -- as will our allies, directly responsible for terrorist acts.' "

Despite all the apparent planning, Boucher said that the State Department does not have "any specific and credible information that would affect the public on imminent attacks." He said a distinction should be drawn between a pattern of surveillance and "specific information that an attack might occur at a given moment, at a given place."

The State Department has issued several advisories since the invasion of Kuwait, warning of the risk of terrorist incidents against American interests overseas and urging Americans in foreign countries to "exercise caution, particularly when in or near U.S. military or civilian facilities or at other facilities commonly identified as 'American.' "

Iraqi rhetoric, in turn, appears to have escalated as the United Nations' Jan. 15 deadline for withdrawal of Iraqi forces from Kuwait approaches. One of the Iraqi diplomats expelled from Britain last week, press counselor Naiel Hassan, told reporters that "if Iraq is going to be attacked, all Western countries will have targets to be hit, and Britain has aligned itself with Americans in this warfare."

When asked if there were Iraqis prepared to carry out the attacks, Hassan said: "Every Arab person living abroad will do that. It is not a matter of Iraq pushing them, it is a matter of belief."

In a speech broadcast yesterday, Saddam took the same tack, saying that Iraq's battle would cover "the whole world," relying on "every struggler and fighter whose hand can reach out to harm . . . aggressors."

Iraqi officials have announced that 350 delegates from Islamic movements in more than 17 countries would meet in Baghdad Wednesday for a three-day conference and draw up a plan for a Moslem response to an attack on Iraqi forces.

Staff writer Al Kamen contributed to this report.