He implores his youthful listeners to believe him when he says that usually isn't the way things happen, "usually government is a process of basic decency."

Belmont High School, 500 humanities students in the auditorium.

Vietnam is never mentioned in the dozen or more predrafted questions a three-student panel asks McNamara, a former defense secretary. He is a solitary figure stage center, fielding gentle if general questions about economy, foreign affairs and his own background. He has arrived under the protective cloak of local police and until his appearance on stage was sequestered with the principal and an assistant. Now he is addressing the audience.

The closest he gets to defining his role at the Defense Department is a somewhat vague explanation of "ethics" in foreign policy ("no different from ethics in another policy") and the role he played in shaping foreign policy.

"The State Department thought we played too much," he says, laughing a little, "but not Dean Rusk. We in Defense were playing our roles as junior partners -- you can't have independent defense policy. The defense secretary is a servant of the secretary of state. It was an easy role for me though it hasn't been so easy for some of my successors."

Later, out in the hall as McNamara disappeared with the accompanying police escort, Bobby Greene, a junior, is saying he had wanted to ask about Vietnam but that he and the others in the audience had been allowed no input in the question-drafting process.

Another student, Mark Aurelio, also a junior, is saying "I don't know it was right that we weren't able to ask about his failures as well as his successes."

Carol De Fontaine, a teacher who helped coordinate McNamara's appearance, denies there were any prearranged ground rules set by McNamara on the Vietnam question. But Tom Ryan, a senior who was one of the 2,600 students not permitted to hear McNamara, says the questions were screened. "i asked the kids on the panel and they said they could not ask about Vietnam."

Brookline High School, 25 advanced history students in room 247. Schlesinger, historian and JFK intimate, is seated at the wooden desk in front of a chalk-smudged blackboard, looking like an authentic teacher. He is wearing a blue polka-dot tie, gazing at the walls and thoughtfully answering "what if" questions. What if, for instance, JFK had lived to be president through the Vietnam war and the '60s?

"I think," Schlesinger tells the questioner, one of 2,200 students in the largely affluent high school, "that the evidence is fairly clear that it is John Kennedy who could have pulled out of the war after the 1964 election. Kennedy had the capacity to refuse escalation. So much of the hysteria of the '60s seemed to stem from Dallas itself. After the murder of John Kennedy, things seemed to unravel."

None of the students challenges this view of the decade of their childhood. Neatly dressed in ironed blue jeans, straight-leg corduroys and turtleneck sweaters, they look at Schlesinger with solemn respect, and at one point, several bring up his book "The Age of Jackson," which is on their reading lists. Another asks the inevitable Teddy question.

"I've retired from politics, so I really don't know very much," he answers. But if he becomes a candidate, I will be for him."

Madison Park High School, an auditorium of almost 200 blacks and a handful of whites. Shriver, the former Peace Corps director and traditional liberal advocate for the poor and minorities, is about to speak first-hand to some of these underprivileged.

"I've never heard of him," says Suzzette Waters, 16.

Here in the Roxbury suburb, racial tensions are close to the surface. About 150 while students staged a walkout earlier in the day, marching to City Hall in a protest triggered by a recent shooting.

Ted Kennedy was the scheduled speaker, but a last-minute switch brought Shriver instead.

"Who's he?" asks Michael Abban, 19. "like what's his view -- liberal, Republican, conservative? Does he hold an office right now?"

"No," says an 18-year-old student sitting next to Abban. "It's just a title -- Sargent."

Shriver, after a few simple remarks that glorify his dead brother-in-law, takes questions from the students. One of them is from Abban, who asks him, hostiley, about the inequities of busing.

"I think," Shriver says, "that the achievements far outweigh the difficulties. The difficulties always get written up in the newspapers. The achievements never do."

One student reads a movie magazine during most of his talk.

Boston Latin, nearly 1,000 cheering upperclassmen and nearly a dozen Secret Service men. "Jacques Consteau was here a few years ago, and that was interesting," says Susan Cronin, a senior who wants to go to nearby Harvard. "But it wasn't as exciting as this."

The excitement, of course, is generated by jfk's younger brother, who is returning to the academically oriented public high school that graduated his father as well as poets, congressmen and a Supreme Court justice.

The students adore him. "I understand your football team is going to win that game?"

"Good politician," says Cecilia Chan, who is editor in chief of the school newspaper, The Argo.

Kennedy is traveling with Theodore White, a graduate of Boston Latin himself who writes the "making of the President" books. "Teddy and I are getting to know each other a little better as these days are going on," teases Kennedy, the unannounced presidential candidate.

In his speech, Kennedy, like the others, evokes the images of Camelot as inspiration for the '80s. He finishes by quoting Oliver Wendell Holmes. It has a familiar ring. "Are you going to give something back to America," he asks, "for all that it has given you?"

Afterward, 16-year-old Charles Vadala sums up what he heard in Kennedy's message. "He told us," he says, "not to be so cynical. You know?"