Fifteen high school seniors pleaded not guilty Monday to bomb charges after duct-taping alarm clocks to the walls of their northern Westchester school.

Four other seniors from Hendrick Hudson High School did not enter pleas because they did not have attorneys.

The 19 students, who said they were carrying out a senior prank, are charged with placing a false bomb, a felony that carries a maximum sentence of 1 1/3 to 4 years in prison upon conviction. They also face one count of criminal trespass.

The cases were adjourned to next month — after Friday's commencement ceremony, where the 19 will graduate but not be permitted to attend.

Dozens of other students have been ordered to perform community service for donating money for the prank or helping buy the clocks.

Defense attorney John Sarcone said he and the other attorneys "hope to have this resolved before the kids go off to college."

"The school district should say you're innocent until proven guilty and therefore we are not going to judge you and we're not going to suspend you and we're not going to banish you from your graduation," said Sarcone. "I would ask that they reconsider and let these kids go to their graduation, and later on, people will be found either innocent, guilty or somewhere in between."

On June 10, students sneaked into the school and fixed 20 clocks to the hallway walls with duct tape, setting all the alarms to go off together at 9:15 a.m. the following day, after the start of classes, police said.

But the plan was foiled when motion-sensing alarms in the school went off, bringing police and eventually bomb-sniffing dogs to the school.

"You can't take anything for granted as far as a particular device," state police senior Investigator Bruce Cuccia said at the time. "It may look innocent and may not be."

About 50 supporters — family, friends and other seniors — attended Monday's court hearing.

Ariel Billary, 18, said, "The kids have worked for four years to graduate and the parents are waiting to see them on this day and it's just taken away from them."

"I learned in high school that you're innocent 'til proven guilty," added Sarcone. "And that's a lesson that I think the school district should adhere to."