The girls who lined the driveway leading to the Humphrey Building had waited for some time on an unusually mild and damp January day, clutching their autograph books and watching impatiently for the limos.

The first to arrive contained a photographer, a reporter and publicists. The second, turning in a moment later, was the one they wanted. Inside was a slender young ex-guitarist named Johnny Depp, who plays Officer Tom Hanson on Fox Television's "21 Jump Street" Sunday nights. From behind the protective rope, the squeal-decibels rose: "Ohmygod! There he is! Ohmygod!"

Depp, who had small parts in "Nightmare on Elm Street" and "Platoon," appears on "Jump Street" with three other actors who get equal billing. The fans were reminded he wasn't the only star on the show. They would have none of it: In one voice they shouted, "But Johnny's the only one who matters!"

Depp, wearing a white tee-shirt with the Edelbrock manifolds logo, jeans torn at the ankle inseam, worn black leather boots, a silver-buckled black leather belt, brown leather buckled wristband and a beige felt hat, emerged to a protective cocoon of guards.

In Washington for only his second visit (his band, The Kids, played at The Bayou several years ago), Depp made his way down the row surrounded by guards, photographers, publicists and sound men bearing long-handled boom microphones.

A 14-year-old from Key Intermediate School in Fairfax County held tight to a single rose wrapped in clear plastic. She'd have to stay after school to make up for cutting class today, she admitted. But catching a glimpse of Depp was worth it.

Depp and company moved into the lobby where more admirers waited, then arrived at the seventh floor offices of Dr. Robert E. Windom, assistant secretary for health. Windom and Surgeon Gen. C. Everett Koop would stage a short news conference with Depp and "21 Jump Street" creator/produced Patrick Hasburgh, then film a public service announcement to be aired after the show's Feb. 7 episode.

The story that night will stress understanding for AIDS patients. The PSA will feature Depp, star of that episode, who introduces Windom, who gives the spotlight to Koop, who offers the AIDS hotline number (1-800-342-AIDS).

Seated between the two sturdy, bespectacled older men -- Windom, 57, wearing a three-piece suit, and Koop, 71, in his Public Health Service uniform -- Depp looked younger than his 24 years. His earring caught the light; a jacket covered the tattoo on his right arm.

He told reporters that he didn't know a great deal about AIDS and had no friends with the disease, but called it "a very scary, serious disease. I don't know much about it and I'd like to learn as much about it as I can." Later he said, "People have to take responsibility for their own actions," he said. "If you play, you gotta pay."

Koop, who advocates early sex education and condoms for the sexually active, noted that "teen-agers don't swoon when I walk down the street," but said that he was appearing "so that we can get a message across." Public service announcements on "21 Jump Street" have been credited for increasing calls to 800-numbers up to four times the hotlines' customary rates.

Windom, who once had his own television show, "Medical Viewpoint," in Sarasota, Fla., gave Depp a blue tee-shirt that said: "Windom's Warrior Against AIDS." Depp gave Windom and Koop leather-sleeved high school letter jackets, with the words "21 Jump Street" in yellow on a red background.

Koop, of stern demeanor and steel-gray square-cut beard, has made many television and taped appearances during his AIDS crusade. He has also waged a battle to get Public Health Service officers into the military uniform he wears. He inspected the jacket, allowed himself a smile and quipped: "Well, it'll never be the uniform of the day."