LITTLETON, Colo. (AP) - Two young men in fatigues and black trench coats attacked fellow students with guns and explosives in a suicide mission at their suburban Denver high school yesterday, and the sheriff said 25 people might have been killed. The gunmen were found dead in the library.

Several students said the killers were gunning for minorities and athletes.

The gunmen - both juniors at Columbine High School - were found dead of self-inflicted gunshot wounds, with what appeared to be bombs around their bodies, sheriff's spokesman Steve Davis said.

"It appears to be a suicide mission,'' Sheriff John Stone said.

The gunmen's names were not released, but students said they apparently belonged to a clique of outcasts called the "Trench Coat Mafia'' who wore long black coats every day, boasted of owning guns and disliked African Americans and Hispanics.

Davis said the motive for the attack was unknown and that school officials had had no reports of trouble from the students.

At least 20 people were wounded at the attack, which began at 11:30 a.m. Bullets ricocheted off lockers as the gunmen opened fire with what students said were automatic weapons. One girl suffered nine shrapnel wounds.

"At first we thought it was fireworks, then we saw them shooting,'' said Jake Apoeaca, 16. "He saw us and then he started shooting at us. Then a guy in a white T-shirt threw two hand grenades on the roof. We hit the ground and then we started running.''

Many students sprinted for the exits. Dozens of students hid in classrooms before escaping with the help of police in an armored car. Others were trapped for hours while SWAT teams searched for the gunmen.

At one point, a bloodied young man dangled from a second-floor window, his right arm limp, and was helped down by two SWAT team members. His condition was not immediately known.

The sheriff said 25 people might have been killed, students and teachers alike. But by early evening, officers had yet to remove any bodies because of the danger of explosives and the need to preserve evidence. FBI agents and police SWAT teams slowly made their way through the building.

"It's just going to take us some time because of how many rooms we have bodies in,'' Davis said.

A third young man was led away from the school in handcuffs more than four hours after the attack. Davis said the young man was believed to be a friend of the gunmen but did not take part in the attack.

Wes Lammers, 17, was among several students who said the gunmen were targeting minorities and athletes at the 1,800-student high school.

Students said the killers might have been part of a group of eight to 10 students known as the Trench Coat Mafia.

Sean Kelly, 16, said several members of the Trench Coat Mafia had a video production class and made a video about guns they had. He also said several members recently bragged about getting new guns and that he heard members making derogatory remarks about African Americans and Hispanics.

In Washington, President Clinton said: "Perhaps now America will wake up to the dimensions of this challenge, if it could happen in a place like Littleton.''

For hours after the attack, wounded victims lay inside the building and police were unable to get to them because they feared the gunmen might still be alive and holding hostages.

Outside, hundreds of officers from throughout the Denver area surrounded the school. Frantic parents were sent to a nearby elementary school, where they searched for word of their children. Some students had called their parents on cellular phones from inside the building.

Students who fled the building wept and held their hands above their heads while police frisked them.

Three youths wearing black - but not trench coats - were stopped by police in a field near the school. State law officers said the three were friends of the gunmen and were being taken in for questioning.

Witnesses said the shootings took place at various places around the school, including in the cafeteria and library.

"They walked down the stairs and they started shooting people,'' said a student who gave her name as Janine. "We didn't think it was real and then we saw blood.'' Her voice broke with anguish as she spoke.

She said it was two young men wearing black trench coats.

"They were shooting people and throwing grenades,'' she said. "Me and my friends got to my car and drove off. ... We saw three people get shot. They were just shooting. Then something blew up.''