Vandals torched two military vehicles and defaced a recruiting center in San Jose on Monday, spray-painting an ominous warning across the building: ``Pre-emptive Attack.''

San Jose fire officials said the targeted vehicle was a minivan wrapped in military slogans and patriotic advertisements. Flames also spread to a second government car parked next to it.

The motive behind the arson remained unclear, though some officials privately acknowledged the graffiti could mean it was a reaction to plans being made to wage war against Iraq. President Bush has argued that a pre-emptive strike is justified because Iraq has been trying to acquire weapons of mass destruction and has denied access to weapons inspectors.

``It's hard to know what this means,'' said Marti McKee, a spokeswoman for the federal Bureau of Alcohol, Tobacco and Firearms. ``Maybe there's a political motive for this,'' she said. ``Maybe somebody has a grudge. It's hard to speculate.''

The fires started about 4:15 a.m. in the parking lot behind four recruiting offices on McKee Road occupied by the Air Force, Marines, Navy and Army. The perpetrators bashed in the door of the Air Force office and broke the Navy's glass door, which was starred and shattered in three spots.

The Air Force office was the only one broken into. FBI investigators took evidence from the office, but officials wouldn't say whether anything was stolen, or whether the arsonists may have tried to burn the building.

Army Capt. Barbara Streater said the San Jose recruiting office had received no threats before Monday morning's attack, and she knew of no other time when it had been vandalized. This is the worst incident aimed at the armed forces in the Bay Area in at least a year, she said. Other recent incidents were the thefts of an Army vehicle and gas tank caps, and cars scratched with keys.

``This is a threat,'' said Streater, referring to the words ``Pre-emptive Attack'' that were painted in foot-tall, red letters on the side of the small commercial building.

``If you look at it in military terms, it means there is more to come,'' she said. ``This time it was vandalism. But what's next? We're concerned about our employees.''

The intersection of McKee and Jackson, which is near Interstate 680, is well traveled -- even in the early-morning hours. There are several round-the-clock businesses. But an employee of one of them, a doughnut shop directly across from the targeted center, said the parking lots are dark and it's impossible to see what's happening there.

Betty Ho, who works at the 24-hour World Gas station next door to the recruiting complex, said a customer saw smoke rising from the parking lot and yelled for the clerk to call 911. But neither the customer nor the employee saw anybody in the area, she said.

As agents from the Federal Bureau of Investigation were combing through the scene Monday afternoon and canvassing the neighborhood for anyone who might have seen those who committed the crime, ATF and San Jose arson investigators were dismantling the minivan.

The vehicle burned to the ground; its steering wheel was burned off and the seat frames were left exposed. Army officials said the van was a few months old and was wrapped in insignia, including the slogans: ``Go Army'' and ``Army of One.''

It served as a mobile advertisement, said Streater, and recruiters drove it to area high schools to promote careers in the Army.

The other car, a sedan with government license plates parked next to the van, was also destroyed and was primarily used to transport applicants to testing centers.