In chilling home movies in which they acted out their attack--and laughed at and mocked those they planned to kill--Eric Harris and Dylan Klebold left behind a stark document that spelled out for authorities their motivation and the methods they used in their shooting rampage at Columbine High School.

In the videotapes shown to reporters here today, Harris and Klebold said they hoped to carry out the biggest mass murder in U.S. history. At times speaking directly to law enforcement officials, the teenagers meticulously recount how they obtained the four guns and built the bombs they used to kill 12 classmates, a teacher and, finally, themselves. The hours of tape are filled with profanity and tirades against homosexuals, blacks, women and Jews.

In one session taped March 15, viewers are given a disturbing look into the minds of the teenage killers. Lounging on reclining chairs in the Harris's basement, the shooters speak of their rage, fueled by what they say were years of taunting from athletes, rich kids and peers only interested in conformity. Their hate-filled conversation includes a discussion about how they planned to blow off one classmate's jaw and scalp another.

"I hope we kill all 250 of you," said Klebold. "If you could see the rage I've built up over the years."

Harris, swigging from a bottle of Jack Daniels and lovingly handling a sawed-off shotgun he named Arlene, said, "I'm really sorry about all of this, but war's war."

Three videotapes Harris and Klebold prepared in the months before the April 20 attack were found at Harris's home soon after the carnage. They are startling in the gunmen's matter-of-fact recitation of what they intended to do to those they believed had wronged them.

At one point, Harris begins to list every girl who declined to go out with him. He muses about dying and becoming a ghost, and the two guffaw about haunting the survivors of their shooting spree, making noises that will trigger flashbacks and "drive them insane."

Also shown today was a black-and-white surveillance tape from the Columbine cafeteria, where pipe bombs were detonated and fires broke out at the start of the rampage. The silent tape depicts the busy lunch-hour cafeteria where the gunmen had placed the largest bombs. With a time display showing 11:25 a.m., flashes are shown and students dive under tables. Smoke billows and obscures the camera, muting the bright strobes of fire alarms.

After a fire breaks out, most of the students race out of the lunchroom and up a flight of stairs. At one point, a man walks through the frame and an explosion blows him off his feet.

Harris and Klebold enter the cafeteria twice. Brandishing their guns, they thread their way around overturned chairs and Harris stops to drink from an abandoned soda cup. Six students huddled under a table go unnoticed by the gunmen.

The existence of the videotapes was not publicly known until last month. Excerpts from the tapes were read at the sentencing of the man who sold the pair the TEC-DC9 assault pistol that Klebold used during the attack. At the time, authorities said they didn't want to release the tapes because they might bring the gunmen the notoriety they sought.

Jefferson County officials made an abrupt turnaround today after Time magazine published a detailed account of the massacre based on the tapes the sheriff's office provided. A sheriff's spokesman said the department felt obligated to share the tapes with the news media and the victims' families, although no video or audio recording of the tapes was allowed.

Families of the victims had been asking authorities for months to view the tapes but had been rebuffed. Sheriff's officials today apologized to the families for releasing the videos during the holiday season. Authorities said they hope to complete an official report next month.

The tapes reveal the pair's fascination with weapons and detailed knowledge of the armaments they had amassed. In one segment, they lay out all the pipe bombs, homemade grenades, ammunition, knives and guns on the floor, fanning them out in a fancy display. On a video tour of Harris's room, with lighthearted narration from both young men, desk drawers are filled with bomb-making material, a closet holds combat knives and guns and gunpowder are stored in a coffee can.

Harris waves his journal and suggests to law enforcement officials that if they want to know what led him to plan a bloody rampage, they should simply "read this."

A few weeks before the attack, the two perform an elaborate fashion show, modeling appropriate clothes and donning bandoliers holding spare ammunition, bombs, knives and guns. Both pose for the camera, mock-shooting their guns at the lens and then whooping after the "kill."

In the last snippet of tape, a one-minute segment shot on the morning of their rampage, Harris and Klebold are dressed and ready for "our little Judgment Day."

Both teenagers are tense, and Klebold is seen pacing. He looks into the camera and bids his parents farewell, saying: "I didn't like life too much. Just know I am going to a better place than here."

Harris says tersely, "That's it. Gotta go. Goodbye."

CAPTION: School surveillance video captures the gunmen rampaging in the cafeteria.