LOS ANGELES — R&B singer D'Angelo urged high school students to speak out against gun violence as he announced plans Wednesday for a 23-date summer tour co-sponsored by the anti-violence organization PAX.

"I want everybody to yell at the top of their lungs. ... 'Stop the violence!' " he told the several hundred students packed inside the auditorium at Hamilton High School.

On D'Angelo's count of three, the crowd obliged his request, their voices reverberating throughout the auditorium.

Clad in a white tank top and baggy jeans, the singer began his brief address by expressing his excitement about the tour, which will be co-sponsored by Levi-Strauss and will kick off July 29 in Chicago and conclude Sept. 4 in Atlanta.

"On the real side," he said, motioning with his hands for the crowd to quiet down and listen, "there's an important reason why I'm here. And that's to support PAX."

As a finale, D'Angelo signed this year's "Levi's Denim Wall," a large piece of dark blue denim that spanned most of the high school auditorium's stage and is serving as a petition for stricter gun legislation. Hundreds of students followed suit, adding their signatures in white ink. Fans attending the concerts this summer may also sign the wall, while others can sign a virtual wall at www.levi.com.

D'Angelo (born Michael Archer) released his second album, Voodoo, earlier this year. It features the single "Untitled (How Does It Feel)" (RealAudio excerpt).

"Where I live, we lose people day in and day out," said 17-year-old Richard Mundy, a junior at Hamilton. "It's good to see that D'Angelo is supporting this, that he really does care."

D'Angelo's appearance came shortly after an impassioned speech by Devon Adams, who was a student at Columbine High School when two students shot and killed 12 classmates and one teacher in April 1999.

"I could ask for a moment of silence for the people who died," the 17-year-old Adams said. "But I don't want silence. I want you guys to get loud. You each have a voice. ... Tell those guys at Capitol Hill that we're not going to take this anymore. We're not going to let our friends die."

Adams, who lost two close friends in the tragedy, traveled to Washington, D.C., to speak to President Clinton and Vice President Al Gore and gave a speech on the steps of the Capitol about the need for more firearm legislation.

Also among the speakers was PAX co-founder Daniel Gross, whose younger brother, Matthew, was critically wounded in a 1997 shooting atop the Empire State Building.

Calling gun violence a "public health epidemic," Gross said, "Every day in America 11 children are killed by gunfire. A Columbine happens in America every day."

"The greatest hope is you," he said. "It's time for all of us to stand up."

PAX did a similar sponsorship with pop-rockers the Goo Goo Dolls last summer and was involved with last month's anti-gun-violence Million Mom March.

D'Angelo tour dates:

July 29; Chicago, Ill.; Chicago Theater

Aug. 1; Denver, Colo.; Paramount Theater

Aug. 3; Phoenix, Ariz.; Celebrity Theater

Aug. 4; Los Angeles, Calif.; Greek Theater

Aug. 5; San Diego, Calif.; Open Air Theater

Aug. 7; Las Vegas, Nev.; House of Blues

Aug. 9; San Francisco, Calif.; Concord Pavilion

Aug. 10; Sacramento, Calif.; Memorial Auditorium

Aug. 12; Portland, Ore.; Arlene Schnitzer Concert Hall

Aug. 13; Seattle, Wash.; The Pier

Aug. 16; Minneapolis, Minn.; Orpheum

Aug. 18; Indianapolis, Ind.; Murat

Aug. 19; Detroit, Mich.; Chene Park/Fox Theater

Aug. 20; Cleveland, Ohio; Nautica/State Theater

Aug. 23; Buffalo, N.Y.; TBA

Aug. 24; Atlantic City, N.J.; Trump Taj Mahal

Aug. 27; Oakdale, Conn.; Oakdale Theatre

Aug. 28; Boston, Mass.; Fleet Boston Pavilion

Aug. 29; New York, N.Y.; Garden State

Aug. 31; Baltimore, Md.; The Pier

Sept. 2; Sunrise, Fla.; Musical Theater

Sept. 3; Orlando, Fla.; Bob Carr

Sept. 4; Atlanta, Ga.; Chastain Park