GREEN BAY, Wis. — Three teenagers accused of helping to plan a Columbine-like attack on a high school pleaded no contest yesterday in separate plea agreements. William Cornell, 18, pleaded no contest to conspiracy to commit homicide, possession of explosives for unlawful purposes, and possession of a short-barreled shotgun.

Shawn Sturtz, 18, pleaded no contest to conspiracy to commit homicide, while Bradley Netwal, 19, pleaded no contest to conspiracy to damage property with explosives.

The three were accused of making bombs and collecting guns to carry out the attack at the northeastern Wisconsin school. They were arrested last fall after a fourth teenager, who was not charged, told an associate principal at East High School about the plot.

Prosecutors say the three teens wanted revenge for bullying and other problems they had at school. Cornell and Sturtz had long been fascinated by the April 1999 Columbine massacre in Littleton, Colo., in which two students armed with guns, knives and bombs killed 12 classmates and a teacher before killing themselves, police said.

Each had charges dropped against them as part of plea deals. Brown County District Attorney John Zakowski dropped a charge of conspiracy to damage property with explosives against Cornell; a charge of conspiracy to commit homicide against Netwal and a charge of conspiracy to damage property with explosives against Sturtz.

He recommended eight years in prison and 12 years of supervision for Cornell, two years in prison and three years of supervision for Netwal and four and a half years in prison and five and a half years of supervision for Sturtz. Sentencing dates were set for October.