A group of FBI counterterrorism analysts warned this week of possible terrorist attacks in New York, Los Angeles and Chicago around Sept. 11, the NEW YORK TIMES is planning to report on Friday, but officials cautioned that they were skeptical about the seriousness of the threat.

The warning grew out of intelligence developed from an overseas source indicating that terrorists might seek to steal fuel tanker trucks in order to inflict "mass casualties" by staging an anniversary attack, officials said.

The information led FBI joint terrorism task forces in Los Angeles and Newark, N.J., to alert other government and law enforcement officials privately this week about the threat, law enforcement officials said. Several government officials in Washington who were briefed on the threat said it was described as credible and specific enough to warrant attention.