For the latest coverage of the tragedy in Littleton, Colo., see our coverage in The Boston Globe's Boston.com. Wednesday's coverage -Rampage reconstruction -Families mourn victims -Colo. gun law debate -What went wrong? -False 'warnings' on AOL -Clinton speaks on massacre -World reactions Globe coverage -Need for prevention -TV coverage -'A suicide mission' Background -Map of Littleton -List of injured -Shooting chronology -Past school shootings -What was 'Trenchcoat Mafia'

WASHINGTON - Half a continent away from the tragic scene, President Clinton and his Cabinet today mobilized what help they could offer grieving Littleton, Colo. - and to ''hammer home to all the children of America that violence is wrong.''

''All of us are struggling to understand exactly what happened and why,'' the president said.

Clinton, who canceled a celebratory political trip to Texas today and moved up a Thursday meeting with British Prime Minister Tony Blair, weighed traveling to suburban Denver to comfort victims of the massacre inside Columbine High School. ''For now, when the school has apparently just been killed with bombs and not all the children who were slain have been carried out, I think it is important on this day that we continue to offer the people of Colorado, the people of Littleton, the families involved the sure knowledge that all of America cares for them and is praying for them,'' Clinton said.

Spokesman Joe Lockhart said no decision has been made on travel. ''There's obviously time on the schedule,'' he said.

''The president wants to do what's best for the local community. ... We are especially sensitive to not causing any disruption or distraction to the ongoing efforts there.''

Grief counselors, at Clinton's command, stood ready to make the trip when called.

''Perhaps the most important thing all of us can do right now is to reach out to each other and to families and their young children,'' Clinton said at the White House, addressing the tragedy for the second time.

He said children all over America need to be reassured of their safety. ''We also have to take this moment once again to hammer home to all the children of America that violence is wrong.

''And parents should take this moment to ask what else they can do to shield our children from violent images and experiences that warp young perceptions and obscure the consequences of violence - to show our children by the power of our own example how to resolve conflicts peacefully.''

Officials from the departments of Education, Treasury, Justice and Health and Human Services and from the Federal Emergency Management Administration held a conference call this morning on what aid they could give Jefferson County, where Columbine High is located.

Education Secretary Richard Riley consulted the local school superintendent by phone.

''From the position of the federal government, we would acknowledge that there are limits to what we can do,'' Lockhart said. ''But there certainly should be no limits to what we try to do.''

Clinton spoke to the nation Tuesday night after he was assured the last of the gunshots had been fired inside Columbine. He was somberly mindful of the earlier tragedies at schools in Springfield, Ore.; West Paducah, Ky.; Edinboro, Pa.; Jonesboro, Ark.; and Pearl, Miss.

Pressed by reporters to say what the government might do to stop such school violence, Clinton said the Colorado community was ''an open wound'' needing time to grieve.

He had been scheduled to celebrate the new Austin-Bergstrom International Airport in Texas today and to star at political fund-raisers in Austin and Houston. The president felt it was ''better and more appropriate'' to remain in Washington, Lockhart said.

Six months ago, Clinton - with Vice President Al Gore, first lady Hillary Rodham Clinton and about 800 educators and law-enforcement officials - held a White House conference on school violence.

Tuesday night, after hours of nonstop television coverage of the dramatic events in suburban Denver, Clinton acknowledged the nation has made little progress. And he was asked whether he still believed his administration's contention last October that students are still safer sitting in a classroom than they are walking down the street. ''Statistically, for all the whole 53 million kids in our schools, it's true,'' Clinton said.

But at Columbine High, where the attackers were apparently armed with hand grenades, explosives and high-powered weapons, ''it obviously wasn't true there.

''That was obviously the most dangerous place in Colorado today.''