The nation's major television networks, in concert with the White House, will blanket the airwaves tonight with a message urging parents to talk with their children about violence in the wake of shootings at public schools and a community center.

In the public service announcement, to air on more than two dozen networks between 8 and 9 p.m., President Clinton says: "Our children need our help to deal with tough issues, like violence. Please, talk with your kids."

The Ad Council calls the coordinated effort "unprecedented," saying it will reach millions of viewers during tonight's "family hour" of TV programming. The announcements will continue airing at various times throughout the year. But some of the campaign's supporters acknowledge that it offers few specific suggestions for parents, and note that it is designed more to ease the fears of preteens than to try to avert youth violence.

The "Talk With Your Kids" campaign grew out of a May meeting at the White House in which the Clintons urged movie makers, TV programmers and other media leaders to consider whether their products encourage or glorify violence among young consumers. The meeting was called in the aftermath of the April shootings at Columbine High School in Littleton, Colo., which took 15 lives, including those of the two teenage gunmen.

Since that time, a teenager shot and wounded classmates at a Georgia school, and a neo-Nazi gunman wounded several children at a Los Angeles Jewish community center before killing an Asian American postal worker.

The 30-second public service announcement was shown yesterday at a White House event featuring the president and the first lady, who has made tougher gun control laws a centerpiece of her all-but-announced bid for a Senate seat from New York.

The first lady rebuked House Republicans who have rejected the administration's efforts to tighten firearms laws, such as requiring criminal background checks for prospective buyers at gun shows.

"After the shootings in Littleton, many members of Congress did say 'enough,' and the Senate passed tough new provisions, proposed by the president, that would have strengthened our country's gun safety laws," Hillary Rodham Clinton told dozens of supporters. "But even these most common-sense of measures--that in no way would have restricted the activities of honest and legitimate gun owners--were blocked by a majority in the House who apparently were and are more interested in the approval of the National Rifle Association than in the safety of our children."

The president told the audience: "Will this public service ad get every parent in America and every child to talk about every dangerous thing that happens at every school? No, but it will have a huge impact."

He said schoolchildren should worry about piano recitals and athletic events, not gun violence. "We ought to give our kids back their childhood, and we can do it, if we do it together," the president said.

The public service announcement features several children making brief comments about potentially violent incidents, such as: "There was this kid that was like 17. He came to school with a gun." The president, appearing at the end, simply asks parents to talk with their children about violence. The ad invites viewers to call 1-800-CHILD-44 for booklets on the issue.

One of the brochures says, "Research shows that children, especially those between the ages of 8 and 12, want their parents to talk with them about today's toughest issues, including violence." A typical conversation, it says, might involve a child noting that in movies, stars such as Steven Seagal and Arnold Schwarzenegger "fight all the time, and everybody says they're heroes. How come?"

The suggested reply is: "The people you mentioned are actors playing a part. If they acted like that in real life, they'd probably be in jail or dead. I don't think anyone who relies on violence all the time is very smart or brave at all."

CAPTION: At the White House, President Clinton promotes a public service announcement campaign that begins tonight on more than two dozen television networks.