By Michael Romano
Denver Rocky Mountain News Washington Bureau

WASHINGTON -- A somber President Clinton offered a personal prayer Wednesday to the victims of the Columbine High School massacre, calling for a moment of silence during a speech to White House volunteers.

"I think it is important on this day," said the president, eyes downcast, "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."

The president, joined by first lady Hillary Rodham Clinton, made an unscheduled appearance in the Old Executive Office Building's Presidential Hall to address about 160 White House volunteers who were expecting a few words of praise for their yearlong contributions from White House chief of staff John Podesta.

Instead, Clinton -- on hand only because the massacre forced him to cancel a trip to Texas -- addressed the bloody siege that has now claimed at least 15 lives.

"It happens that this day was scheduled on what turned out to be a very sad day for America," Clinton said.

Calling the volunteers "the best of American citizenship," Clinton said it is vital to remember that the nation must "come together and pray together -- but also commit to act together" to deal with tragedies like the siege at Columbine High School.

Clinton, who said the "horror and agony" of the tragedy "bring us together as a national community," praised the work of the police officers, the students who risked their own lives for classmates and the doctors and paramedics who helped the wounded.

"I have been particularly struck by the story of Mrs. (science teacher Theresa) Miller, the teacher who heard the gunfire and led dozens of students to safety in the choir room, who worked to keep them calm and quiet for hours while students removed ceiling tiles to let in more air."

Added Clinton: "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.

"It is very important to explain to children, all over America, what has happened, and to reassure our own children that they are safe," he said.

As he did during a White House briefing on Tuesday just hours after the shooting, the president reserved any comments about specific plans on legislation or any executive actions.

"In the days ahead," he said, "we will see what else can be done."

Then the president asked for a moment of prayer, the silence in the hall broken only by the sharp click-click-click of automatic cameras.