Two or three times a week, the Rev. Jesse L. Jackson brings audiences of children to admit their most guarded secrets. He descends on schools in Reston or Omaha or Houston, and in less than an hour he turns adolescent hope into fervor and resolve. Hundreds of teen-agers swear off drugs. And then he leaves.

"It was a day of glory," said 17-year-old Tracy Burnette, remembering Jackson's visit to Largo High School in Prince George's County last October. That afternoon, she stood in a mass of chanting, cheering and crying students who had poured onto the football field in a public admission that they had used drugs or alcohol.

"A lot of people were touched by it," Burnette said, "but I don't think it changed anything. The excitement was here the next day, but then it wore off."

In the year since Jackson came to Spingarn High School in Northeast Washington and launched his nationwide tour of antidrug rallies, his speeches have become familiar and frequent across the country. His staff estimates that he has spoken to as many as 80,000 youngsters.

Last week, his message prompted strikingly similar responses from a moneyed, mostly white audience in Reston, a less well off, mostly black student body in Prince George's and a silent crowd at Gallaudet College, where hundreds of deaf students received his message in sign language.

His cadenced, rhyming admonitions, said an aide, have never failed to bring youngsters forward to confess.

But there is less evidence, say those who remain at the schools, that Jackson's rousing speeches make a lasting dent in the use of drugs -- or that officials at the schools have taken up the crusade he launched.

Jackson does not argue that his hour of truth with these students is sufficient. His purpose, he said, is to expose "a state of emergency" and rely on teachers, principals and parents to follow through. His national organization, Push for Excellence, is attempting to distribute training tapes and organize self-help groups at schools he has visited.

"I have simply pulled the scab off a sore, and now we see . . . there is a cancer," he said.

One student at Largo High School said two of his friends have given up drugs because of Jackson's speech, and many have reduced their marijuana smoking. But most students agreed that within a few days of Jackson's whirlwind appearance, the school was back to normal: dope in the bathrooms, graffiti on the walls and fights in the halls.

Largo High counselor Ralph Amis said the number of drugrelated suspensions at the school has not changed since the Jackson visit. "I don't know whether Jesse Jackson or anybody could make a difference," he said. "I don't think so, not with the kind of kids we're dealing with."

And Largo High Principal Cynthia Payne acknowledged that her school should have arranged counseling or other programs for the students Jackson persuaded to admit their drug or alcohol use. But, like many of the other schools Jackson has visited, Largo did not follow through sufficiently.

At other schools, where the enthusiasm stirred by Jackson is fresher, there is hope that a familiar message will leave a deeper impression when it is borne by a celebrity.

"I'm an optimist," said John Randall, a Reston principal whose eighth grade students heard Jackson last week. "For some students, it will make a difference . . . . Someone's life could have been spared."

Jackson is 40 minutes late and the auditorium at Prince George's Central High School near the District line is pulsing with the noisy, impatient energy of 1,100 teen-agers. They bounce in their chairs, chew gum with vigor and shout over the strains of a student jazz band.

Finally he arrives and the students go crazy. "Jesse, Jesse, Jesse," they scream.

The students ignore the protocol of the moment; they jeer at the National Anthem and laugh at the color guard. When their principal takes the podium, she can barely be heard above the din.

Then it is Jackson's turn to speak, and the jam-packed room falls silent.

He scolds them for their rudeness: "When these young people stand and do the color guard, you owe them your respect and attention . . . . Children cannot justify acting childlike."

A collective guilt passes over the room. Now he has their attention, and the routine begins.

He leads them in a standing, pep-rally-style chant:

"I am," they shout in unison, "somebody."

"I am, somebody."

"My mind is a pearl."

"I can learn anything in the world."

Then he calms them, and it is quiet once more. He tells them of a civil rights movement they have learned about as history. He admits his wrongheaded refusal to learn French. He shares a story about his own experience with drugs, a painkiller he was given after knee surgery. He so craved the drug, he said, that he would have stolen his mother's cheap jewelry to get more.

The students are transfixed. Their legs have quit bouncing; their bright, vulnerable faces are trained on their modern-day hero.

"I am concerned about the collapse in morale and moral character," he says. "This rise in cocaine and drug use is of epidemic proportion." Now he is booming in his pulpit voice: "You must say no to drugs. No to liquor. No to making babies without love. No to violence."

The message hits hard at a school that just days before had lost a promising senior who choked to death on her vomit after drinking a bottle of whiskey.

In a different room before another audience, Jackson's performance could be a stump speech on the campaign trail. He poses for photographs with the babies of faculty members, shakes a sea of outstretched hands, signs autographs and, before he leaves, ushers off dozens of students so they can register to vote.

He exits, wiping the sweat from his face, flashing the thumbs-up sign. On the ride back to his hotel he is philosophical, explaining in a raspy voice the constant focus of his speeches.

"We've got a generation of youth now who are craving liquor as a form of anesthesia, driven to drugs as a form of anesthesia . . . . Gramm-Rudman-Hollings, Reagan's budget . . . can only be fought by people who are alert and sober and sensitive."

Three thousand Reston students perch on metal bleachers at South Lakes High School. They are the children of ambassadors and members of Congress; they go to school with braces on their teeth and clothes recently off the rack. Just over 10 percent are black, 80 percent will go to college.

"In a suburb, people think the kids are innocent," said sophomore Janine Sherman after Jackson's pleas emptied three-quarters of the stands. "When you get a whole school to admit they know somebody who died because of drugs, it opens people's eyes. Some people will listen."

Ninth grader Tariq Taylor disagrees. "It you want to do it, you're going to do it. I don't think he can change that."

Peter Hobbs, principal at the high school for deaf students at Gallaudet, said he believes that half of his 400 students use drugs. They are vulnerable, he said, not only because of the frustrations caused by their handicap, but also because they live away from home, on a campus with college students. And they are shut off from many of the drug prevention programs aimed at the rest of the teen-aged world.

The staff was shocked recently when four students were caught with cocaine. But Hobbs was not surprised.

"I was going home and wondering if I was going to learn of a dead kid from an overdose," he said.

The school called Jackson for help. His speech, said Hobbs, would be "the opening salvo of a long war."

Flanked by sign language interpreters, Jackson delivers his standard address, inserting a story about his half sister, Rudell, who is deaf.

"Some people cannot hear with their natural ear," he says. "Others can talk, but have nothing to say." A moment passes as the signers catch up, and then the audience laughs.

At other schools, a wave of nervous chatter typically erupts when Jackson bids youngsters to admit their vices publicly. The kids look side to side, assessing how peer pressure will fall this time. At Gallaudet, hands start moving. Slowly, a few at a time, they go forward.

Several hours later, 18-year-old Patrick McKeever is still carrying around in his gray leather jacket the pledge card Jackson distributed. He has signed it, agreeing that he will "say no" to alcohol, drugs, violence and teen-age pregnancy. But he has not decided whether to turn it in or throw it away.

The scope and finality of the promise clearly gives him pause.

"I won't do any pot," he says through an interpreter, "but it's hard to stop drinking."