The Justice Department tightened security yesterday in preparation for the first anniversary of the bombings of two U.S. embassies in Africa, which killed more than 200 people.

The Justice Department's action came less than a week after the FBI indefinitely stopped public tours at its headquarters building for security reasons, after receiving "unconfirmed threats" linked to Islamic militant Osama bin Laden.

Bin Laden has been indicted in the United States for allegedly masterminding the Aug. 7, 1998, bombing of the U.S. embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania. Last month, he was added to the FBI's "10 Most Wanted Fugitives" list.

The Justice Department said it ordered the stepped-up security in all of its buildings even though the FBI has not provided "any specific threat information at this time."

D. Jerry Rubino, a Justice Department security officer, said in a three-page security alert that U.S. government counterterrorism experts considered "anniversary dates a key indicator of possible terrorist activity."

The FBI said its tours, offered to the public since 1937, would be halted to allow completion of its "security enhancements," which began because of unconfirmed threats to its headquarters. FBI officials have declined to give any details of the threats.

The security alert, sent to all Justice Department employees, calls for general security measures to be put into effect immediately. Among the steps, all employees must display their identification badges in Justice Department buildings, all visitors will be screened by metal detectors and commercial vehicles must be searched before entering the buildings. Most of the measures already are in place at Justice Department headquarters.

Similar warnings were issued on the anniversaries of the Oklahoma federal building bombing on April 19, 1995, and the FBI raid on the Branch Davidian cult's compound near Waco, Tex., on April 19, 1993, which killed about 80 people.