A 13-year-old California boy with a loaded handgun and a hit list of 30 names was arrested at school yesterday - the most serious of another wave of bomb scares and threats to disrupt schools since the Colorado massacre.

Authorities pulled the boy out of class at Sierra Middle School in Bakersfield, Calif., after his classmates said they saw a gun under his shirt and saw him loading it outside. A .40-caliber semiautomatic handgun and 13 rounds of ammunition were found on the boy, said Kern County sheriff's Cmdr. Don Youngblood.

In the boy's backpack were 30 pieces of paper, each one with the name of a classmate or teacher, a drawing and the words ''because they deserved to die'' scrawled at the bottom, Youngblood said.

In Enid, Okla., a school employee found a pipe bomb in a restroom of a high school yesterday. Classes were canceled for the 1,400 students and state troopers disabled the device.

A middle school in Petaluma, north of San Francisco, was evacuated after five devices that looked like pipe bombs were found in the backpacks of two students. The devices were detonated but contained no explosive material, Petaluma City Schools Superintendent Carl Wong said.

Threats and scares at the nation's schools have intensified since two students killed 12 classmates and a high school teacher in Littleton, Colo.

In Tavares, Fla., a 10th-grader playing hooky yesterday was arrested for making bomb threats that led to the evacuation of 27,000 students from all 39 Lake County schools in central Florida.

A threat found on the Internet led school officials in Sylvania in northwest Ohio to close two high schools for the day so the buildings could be searched. An 18-year-old student was charged for threatening that Sylvania would be the target of a rampage worse than the shootings in Colorado.

The student told detectives the computer message was a prank.

A day after bomb threats at seven Detroit schools, the police chief promised to prosecute those involved.

''The hysteria has got to stop,'' Police Chief Benny Napoleon said.