Three small fires set in trains and the explosion of two homemade bombs at rail stations in the last five days have added to the unease in Japan about the arrival of the new millennium.

Commuters bustled between trains today with loudspeakers blaring cautions, and strode past coin-operated lockers and trash cans that were sealed to prevent anyone from planting bombs inside them.

The incidents and the official warnings they brought came on the heels of the government's mixed messages about possible technological turmoil as the New Year arrives. Officials insist the country is ready for the Y2K computer rollover, but have told people to stockpile food and water, and have placed 96,000 troops on call for New Year's Eve--including teams trained to handle nuclear and chemical accidents. More than 106,000 police officers also will be on duty.

The extraordinary call for manpower and the rash of train incidents has spooked some residents. "I feel, undeniably, that something will happen," said commuter Masao Ikeda, 65, standing next to a bank of sealed coin lockers in a Tokyo subway station. "First, there's the Y2K problem itself. Then there are some criminals who would seize the opportunity to do something and make it look like [it was caused by] Y2K."

"Politically motivated guerrilla groups still are around," agreed fellow commuter Yoshikazu Adachi, 28. "It's kind of scary."

Authorities said they do not know who placed the explosives, apparently packed in small styrofoam balls with timing devices. They said they believe the fires were set by opponents of construction of a controversial second runway at Tokyo's Narita Airport.

One of the explosive devices was found by a locker attendant Monday morning at Urawa station, just north of Tokyo. Two of his fingers were injured when the device went off as he moved it. On Friday, a small bomb exploded in a bin at a train depot, apparently after it had been swept up with the trash from the high-speed Shinkansen train. No one was injured. On Sunday, three fires broke out under seats on trains serving Narita Airport, causing delays but no injuries.

In addition to cautions issued at home, the Foreign Ministry warned that Japanese living abroad and Japanese-affiliated companies should be wary about "becoming entangled" in terrorist incidents abroad.

The warnings have been echoed in the press. The Sankei Shimbun newspaper noted in an editorial today that even extra manpower "cannot oversee all the crowded trains and terminals that will be packed with travelers, and the temples and shrines that several million people will visit."

Prime Minister Keizo Obuchi has sought to portray his government as in control of possible Y2K computer problems . He has been appearing in television ads, unusual for a Japanese leader, but even these messages have been ambiguous. "We don't think any big disruptions will take place, but it is important to be prepared for the worst," Obuchi said in one ad. He went on to urge people to stockpile two to three days' worth of water and food.

Both the central government and the Tokyo metropolitan government are setting up special disaster prevention headquarters to monitor events. Obuchi plans to spend New Year's Eve there and has scheduled a television appearance at 12:45 a.m., in which he hopes to tell the nation that all went smoothly.

CAPTION: Commuters stride past subway luggage lockers that have been sealed to prevent anyone from placing bombs in them.