The "&" was always the most important thing about Peter, Paul & Mary, and as they sprawl on a sofa in their hotel suite, that connective spirit is almost palpable -- in the roll of sentences that begin in one mouth and end in another, in the mix of attention and teasing that surrounds individual pronouncements, in the casual touching, the leaning into warmth, the mini-hugs that seem so easy.

Now, as she has been so often on stage, Mary is in the middle. "I like it this way," she purrs, bouncing gently between the two men who have been in her life for the longest time.

Peter Yarrow, Noel Paul Stookey and Mary Travers, who will celebrate their 25th anniversary with a gala fundraiser for TransAfrica at the Kennedy Center on Tuesday, seem always to have been linked, a musical molecule without surname. "That was a card in Trivial Pursuit," laughs Stookey -- " 'What were the last names of Peter, Paul & Mary?' "

Offstage, Stookey is called Noel ("Who cared what my first name was once the group hit?"). He and Yarrow still look alike, but the look has changed in the past quarter century. The trademark goatees have long since disappeared, as has much of the hair on top of their heads. They both sport polite mustaches and gentle demeanors.

"Which was Peter, which was Paul?" muses Stookey. "Everybody gets confused, even my kids. We really do look alike -- much more than when we began." Travers, on the other hand, seems constant, her blond locks still looking for a wind to blow in.

There is peace here, the sharing of, if not the high ground of the '60s, at least a common ground in the '80s. For much of the '70s, of course, there was no communion, as the trio went three separate ways.

Tuesday's concert, which is already sold out, is expected to raise more than $50,000 for TransAfrica, the Free South Africa Movement organization that has coordinated the year-long series of arrests at the South African Embassy. PP&M's participation, which included being arrested at the embassy in January, is in keeping with their position two decades ago, when their voices reflected social consciousness emerging as a dominant force in popular music. It was a time when a number of folk artists, most notably Bob Dylan, Phil Ochs and Joan Baez, articulated in commercial terms a sense of commonly felt purpose, a time when pop and political cultures intertwined.

The trio sang at the Live Aid concert last summer, though their teaming with Bob Dylan for a "Blowin' in the Wind" finale didn't come off as planned. With Dylan and Baez, they still represent a thread of conscience and idealism that has often run thin in pop culture, particularly in the '70s. But in the wake of Live Aid, Farm Aid and other pop/philanthropic projects, the spirit of musical commitment that PP&M symbolized seems renewed.

"Old folk singers never die," Stookey once said, "they just get asked to do benefits all the time" (it was a benefit, in fact, that brought them back together in 1978 after an eight-year separation). Still, it's hard not to see the trio's currency as somewhat devalued since their heyday, when it seemed they were everywhere, as they often enough were. It would be easy to write them off as simple nostalgia.

The thought provokes a wry smile from Yarrow, who quotes Tom Paxton on the subject: " 'It's okay to look at the past, I just don't want to get caught staring at it.' "

"I think it's demeaning to call anything that feels it belongs to some other time a throwback and dismiss it," Yarrow continues, "and not to understand that there are some battles won, sometimes culturally, sometimes politically, sometimes personally, and that those provide some kind of cultural ethos that can reappear in another form. That era the '60s is never really understood for all its joy, all its freedom, all the good life that was shared in creative terms.

"I really think we were lucky, folks."

The We Decade, he insists, "is not so far away that we can say there is no legacy. There is indeed. And it is a profound source of pride to know that we were part of this very positive thing. When we get on stage in any concert, there is a little bit of its being a march to us, a little bit of the sense that somehow it's going to be a grain of sand, that it's going to make a little bit of a difference. It does link up."

The Kennedy Center show, which will include performances by Harry Belafonte, Judy Collins, Odetta, John Denver and Carly Simon, and tributes from such people as Coretta Scott King, Cesar Chavez, Gloria Steinem and George McGovern, honors Peter, Paul & Mary for "25 years of commitment to freedom, justice and human rights."

Says Yarrow: "We're going to live a night, not of nostalgia, but of continuity, forward motion, reconfirmation. Nostalgia is a good word for some stuff. It's not a good word for what we experience on a day-to-day level."

Mary Travers recalls being asked once by a television interviewer, " 'Well, where are the heroes of the '60s?' And I told her nobody said being a hero was a permanent job."

When Peter, Paul & Mary first got together to perform at New York's Bitter End in 1961, of course, no one was calling them heroic. The group was designed essentially as a Kingston Trio clone with sex appeal, though PP&M ended up closer to the tradition of the Weavers and Pete Seeger (they often referred to themselves as "Seeger's Raiders"). It was the Weavers who, in the '50s, had first proved it possible for folk musicians to experience commercial success without compromising their musical taste or social integrity. They, too, had revealed old songs and new songwriters to a large public, inspiring at least some investigations of the wealth of musical subcultures in America.

In any event, Peter, Paul & Mary had the good fortune to arrive at an auspicious moment, just as the folk revival was attracting listeners disillusioned with nonsensical pop and rock music and unable to relate to increasingly complex jazz forms. Folk music, simple and accessible, took over almost by default.

Travers, an aspiring singer and actress, had just had a Broadway show fold under her. Yarrow, a psychology student, had been teaching folk courses at a New York college and performing solo. And Stookey, whose roots were in rock, had come to New York to find work as a comedian. An agent anxious to cash in on the Kingston Trio craze got them together. Possessed of a smooth image that was equal parts bourgeois, collegiate and Greenwich Village intellectual, they were exactly right for the times.

From the beginning, there was a symbiotic cohesion of what one early critic called "two cellos and the voice of an angel." Recalls Yarrow: "I snapped into an awareness of how voices could feel with one another -- not like a Rothko painting, where one form ends and another begins, but with really clear definition and an egalitarian relationship of parts."

Albert Grossman, who managed Bob Dylan, also managed Peter, Paul & Mary. When they performed live or in the studio, Yarrow says, Grossman "wanted those voices up front, individually heard. He didn't know what he was talking about, but he knew."

Peter, Paul & Mary's svelte three-part harmonies, meticulous arrangements and slick, stylized performances led them to be vilified by purists as "fakesingers" who compromised the integrity of the genre in order to make the music palatable to white, middle-class audiences.

The criticism wasn't entirely without foundation. But ironically, Peter, Paul & Mary not only revived much of the genuine folk tradition, they also popularized a new breed of socially conscious songwriters. Dylan would undoubtedly still be Dylan, PP&M or no, but it was the trio's rendition of "Blowin' in the Wind" that gave his work its first mass audience. (They would later repeat the favor for Gordon Lightfoot and John Denver.)

The most popular and successful group to emerge from the folk revival, Peter, Paul & Mary were also among the first pop artists, as Rolling Stone observed, "to put their popularity at the service of a cause (and vice versa)." Which didn't mean that much of their music was anything more than harmless entertainment, only that enough of it was something more. In the process, many message songs worked their way into the American consciousness.

" 'Hold the fort for we are coming . . ., ' " Yarrow sighs. "The thing that's wonderful about folk music is that it has traditionally played the part of newspaper person, news teller, editorial. It has been the arm around the suffering, it has been a compassionate embrace, whether it's been in black Baptist churches in the South or on the union picket line. Music has always played a part in saying there is a solidarity of caring and you can share this by lifting your voices in song.

"It's very special and it's very special about folk music. You can't disco dance at a march, the music doesn't have what it takes to do it. Folk music, traditional or contemporary, has always played that particular role."

Over and over, "it reinvents itself using the contemporary popular culture. At one time it was opera, or Shakespeare . . . now it's U2 or Sting who take the stage."

Looking back, the struggles of PP&M's youth seem more cultural and generational than political or economic. Social, artistic and political expression all experienced a badly needed renewal after the stifling conservatism of the '50s. But the movement was greatly damaged, Stookey believes, by the assassinations of John F. Kennedy, Malcolm X, Martin Luther King Jr. and Robert Kennedy.

"I really see the '60s as being on a roll, being cumulative, one thing leading to another," he says, "each awareness opening the door to a new awareness. The impact, as it translated through popular music, was that music and real life became very interconnected. There was no separation somehow between the performer and life happenings. And then we got hit broadside with those devastating emotional blows. It was a confrontation with a kind of violence that destroyed the fragile building that was going on, where a vision was being developed wordlessly among a lot of people with no apparent relationship other than the sharing of a vision."

"There was a tremendous pain, grieving, immobility created by those destructions," adds Travers. "It was something that sent the country scurrying back into themselves. Four pivotal leaders, two working-class, were blown away within a very short period of time . . . There was a kind of psychic shock that the nation went through."

"When reality confronted the dream, everybody went into a philosophical nose dive," Stookey says.

Before the retreat sounded, however, PP&M spent most of a decade on the musical ramparts, a presence on radio, records and television, at concerts, college campuses and political rallies, reinvesting in popular song the concern of art for life.

"We're very lucky to have had the music that we've sung become an integral part of the cultural fabric," says Travers, who remembers a friend's daughter coming to a Peter, Paul & Mary concert and saying afterward, "I like them but they've stolen all our camp songs!"

The group was there when it counted: at the Selma to Montgomery march, Martin Luther King Jr.'s 1963 civil rights march on Washington, the 1969 antiwar march (Yarrow organized the entertainment). Over the years there would be a cornucopia of other causes, from the Equal Rights Amendment and human rights to nuclear arms control, so it's little surprise that the group is involved today with antiapartheid work, nuclear freeze events and protests against U.S. intervention in Central America. Stookey's "El Salvador" is one of the most powerful of their new songs, and Travers and Yarrow have both made fact-finding trips to Central America.

"Why I went to El Salvador with my daughter, and what I discovered through my mother, is that you can't just read about it," says Travers, who was arrested at the South African Embassy with not only her musical family, but her mother and daughter as well. "You have to reach for that emotional understanding and make a mesh. If you're a parent and you're concerned about the potential for a nuclear holocaust or you're concerned about the quality of life that your children have, something other than your own closed society, you have an obligation to not only reach out and try to do something, but you have an obligation to take your children with you."

Children are terrified about nuclear war, says Travers, but "they're doubly terrified because they don't see their parents doing anything about it . . . you go on a march with your child, your child perceives you doing something, you become less impotent in the situation . . .

"As a famous 17th-century Hasidic scholar put it, 'It's not your duty to finish the task, it's just your duty not to neglect it.' I don't expect to solve all the world's problems, I just expect to put my two cents in."

By 1970, Peter, Paul & Mary found themselves in stasis, a situation accelerated by Yarrow's arrest on a morals charge involving a 14-year-old girl (he was later pardoned by President Carter) and by Stookey's rebirth as a Christian in 1968. His subsequent insistence on speaking about it from the stage led to some less than ecumenical bickering, but it was just one more symptom, albeit an ironic one, of the major problem within the trio: the need to retain personal identity.

"We needed to watershed individually, personally, creatively," says Yarrow. "It becomes so involuted, such a dismissal of so many of the dimensions inside one that need to grow. It was unfortunate, but from the perspective of having gotten through it and having gotten back together again, it was a terrific thing to have happened."

The group's history, Stookey muses, was "parallel to marriage, probably parallel to every relationship, certainly parallel to bureaucracy, and a symbolic representation of any deeply felt emotional experience. First the experience, then the description of the experience, then the writing of the exprience, then the building of the structures to house the writing of the description of the experience. As the distance from the experience itself increases . . . "

"Does he do one about people?" Yarrow jokes.

"Oh, I've lost it," Stookey concedes, as if the thread was pretty thin to begin with.

"Peter, Paul & Mary at the beginning was an experience," says Yarrow, getting serious again. "It was three individuals together on stage and we made a sound together but we were obviously very different people. After 10 years together, you'd be amazed how similar we had become. We has less to bring individually to the relationship.

"We needed to go out and have an affair," adds Travers. "We were a mid-life crisis."

When they split up, Travers remained in New York and pursued a solo career, hosted a radio show, lectured on "Society and Its Effect on Music" on the college circuit.

Stookey moved to the Maine coast, where he converted a farmhouse into a studio, recording Christian music and producing other Christian folk acts. He also wrote songs, including the beautiful "Wedding Song (There Is Love)," whose more than $2 million in royalties has gone to charity after Stookey refused to copyright it in his own name, believing it was a gift from God.

Yarrow headed for California and remained involved as an activist/organizer, helping to reject the antihomosexual Briggs initiative in 1973 and organizing the first antinuclear Survival Sunday in Los Angeles -- which proved to be the vehicle of reunion. He also wrote the hit song "Torn Between Two Lovers."

Stookey picks up the thread again. "On our albums you could really hear the individuals struggling for their identity, lobbying, exercising their individualty. It's a nice balance now. When we came back together in '78, we knew that being together was important but we didn't know what the result of it would be. At the end of the first reunion tour , we looked at the upside: It was great, it was challenging, there was obviously a constituency out there that shares our concern. The music is still relevant, although it may not be popular.

"What's the downside? Who wants to spend 200 days on the road? Each of us has spent eight years apart from each other, developing a personal relationship with our families and developing a connection with our own integrity. Can you compute that in number of dates?" No, although they're now at 50 a year, up from 30.

"That's where we are now, and it feels good," says Yarrow. "They are a challenge and a thorn in my side. And it feels good." There's no promise of an endless reunion, though Travers believes that "we'll probably be out there with our walkers and canes, shaking our sticks at the Washington Monument."

The tours are now structured so as not to overwhelm their personal lives, which have paid the price over the years. Only Stookey is still married, with three daughters. Travers has two daughters and recently became the group's first grandparent. Yarrow has two children from his marriage to Marybeth McCarthy, Gene's niece. Despite the evident camaraderie, their social lives overlap very little.

What sustains, though, is a belief in the empowerment of song. "I remember when folk music really affected popular music in a profound way," says Yarrow. "The genre itself is a classical genre . . . be people who love it, who get something out of a form that's old. They don't feel nostalgic, they know there's something out of that music which they can expect, they can count on, they know it's going to be there -- a certain level of literacy of lyric, a certain musicality, an overall concern for the human condition . . . "

"The '60s was a period in which ordinaty people felt empowered by circumstances," he continues, "that they had access to the wheels of power and they could make a difference by marching or singing, getting arrested, whatever. In the '70s, there was a sense of disenfranchisement. I think what is happening now is that people feel there is a purpose to writing a song, singing a song, marching on a march, expressing their anger, expressing their concern . . . We see a definite connection to a thread that gets reasserted in its own terms, in its own language, in different periods. "In the '60s," adds Stookey, "if you heard a song by Bob Dylan and then you went to a march and then you heard a newscast, everything seemed to be connected. In the '70s, it was like a cry in the darkness to respond to it on more than a momentary basis . . .

* "Our songs embody the affirmation that the group is most comfortable with, bringing bad news with a ray of sunshine. It's not something we sit down and talk about, but as I look at what we've done and what we continue to do, what we really hope to be is an encouragement to the individual. Not en masse, but is there something that we're doing that provokes in you a desire to settle your shop, get your house in order, take a step forward perhaps in an area that you were reluctant to, or afraid to?"

Those questions are still blowing in the wind.