"Schools don't have much of a moral center anymore," he said. "There was a time a school was a place where a child really had society's values and they had to live by them, or they were told to leave.

"We've tried to make our schools all things to all people, and we've let kids create the culture and the moral system of the school. And now we're just reaping what we've sown," said Mr. Ryan, head of the Center for the Advancement of Ethics and Character at Boston University.

Federal, state and local law enforcement authorities, school officials and behavior experts believe Tuesday's shootings in Littleton, Colo., are rooted in a lack of supervision of children by adults, including parents and school officials who fail to recognize early-warning signs of violent behavior; an easy accessibility to weapons and materials to build bombs; and a culture overwhelmed with images of violence.

Retired Army Lt. Col. Dave Grossman, a former West Point psychology professor, believes efforts must be made to curb the influence on young people of violence in the media.

"Anywhere television appears, 15 years later, the murder rate doubles. We continue to dither around and fail to take action when television is the single most pervasive influence in the lives of children in America. They spend more time watching TV than any other single act," he said.

Col. Grossman said the American Psychological Association and the American Medical Association have warned about effects of violent television on children, "and nobody wants to talk about it." He described Littleton as "straight out of a bunch of movies," adding if children are influenced early, they can become "drawn to the fantasy world that the TV provides."

"Like rats carrying the black plague, the visual media are carriers of this virus of violence," he said.

Herbert Williams, president of the Police Foundation and former superintendent of police in Newark, N.J., said that while a lack of supervision is key, the availability of mood-altering drugs also plays a role in rising violence in the nation's schools.

"We are increasingly on the edge as a society, particularly among the young, who have an extraordinarily high suicide rate. There is an obvious problem and no one knows definitely what is causing it," Mr. Williams said. "Drugs are available, and large numbers of children are taking them, spawned by a fast-paced, jet-set society that glamorizes violence, drugs and sex.

"We need to do a better job of teaching our children the values of our country, but sometimes there is so much sheen and gloss from the surface, it is difficult to penetrate the substantive levels," he said.

Boston University's Mr. Ryan is among several people from around the country who suggest that a pervasive climate of moral decay and lack of responsibility among adults are keys to understanding why such tragedies repeat themselves.

Years ago, he said, schools would not allow students like those of the "Trench Coat Mafia" at Columbine High School to get away with their paramilitary, Gothic dress and constant harassment of other students. Today, schools foster "permissive, flaccid environments," where the rights of children outweigh their responsibilities, he said.

"There is going to be a phalanx of grief counselors who are going to come in and smother this place with this pathetic oozing of sentimental treacle, rather than coming in and saying, 'This is an obviously sick environment, and you've got to change it and provide a structure, a discipline in this school,' " he said.

Studies by American Agenda, a nonpartisan research organization, have shown that while a majority of Americans think children lack discipline and moral values, the public holds parents accountable.

"Large numbers blame irresponsible parents for the problems they see in young people, not schools," said Deborah Wadsworth, the organization's executive director. Equally "painful," she said, is research on parental involvement.

"Parents acknowledge that they are having a hard time parenting," she said. "They often confuse their unwillingness to discipline with the sense that it may be misunderstood as withholding affection. They are not sure what to do to raise morally strong and upright kids who know right from wrong. They want the schools to reinforce the values that kids should learn at home."

Too many parents, absorbed by work and recreation, have taken "a vacation from being parents," Mr. Ryan said.

Lisa Murphy, a researcher at Hamilton Fish National Institute on School and Community Violence, said her organization is working to develop strategies for school-violence prevention. Everyone, from parents and teachers to businesses and law enforcement, must take responsibility for school violence, she said. Youth violence, she notes, is social violence "which happens to be occurring at school."

What can the police do? Try to work with the schools and the communities, Mr. Williams said, and not much else. "We don't want a police state.

"Joint working relationships will make communities safer," he said, adding that he hoped schools tighten their own security and upgrade training to prevent future problems.

But Mr. Williams said changes have to come at the grass roots --neighborhoods, blocks and streets -- and not from the government. "Ultimately, the power in America rests with its people."