When a member of the Chinese delegation to the United Nations asked an American friend not long ago if all American popular music sounded the same - as he supposed from listening to the radio - the friend arranged for the Chinese official to hear an evening of jazz.

He listened with great absorption and then said, "I believe I understand. This is American folk music. It has your own kind of sprit. Are there other original American musical sounds and forms?"

Many, he was told, and in a wide variety of popular as well as folk music. The man from the Chinese delegation has since been looking into this inexpected news about America.

Among the performers I have suggested he hear to broaden his sense of our diversity is James Talley. Not a jazzman, but rather a 33-year-old, Oklahoma-born, popular singer-composer who is a favorite of Jimmy and Rosalynn Carter and millions more Americans.

Talley's music - a blend of country and blues from the South and Southwest - celebrates working people, from truckers to "black lung" miners, telling of the plain, everyday valor that enables them to survive. Just as jazz began by telling of everyday black valor. ANd like black music, James Talley's has deep American roots.

He comes from a long tradition in American popular music - going back to Woody Guthrie and Jimmy Rodgers ("The Singing Brakeman"), and beyond them, to the music-makers of the American frontier who sang of independence and of the hard work, with some whiskey on the side, that might make their dreams take palpable shape.

Dreams power all forms and idioms of popular music. Different dreams nourished by people of profoundly different backgrounds. In what came to be called country and western music, the early dream was of unending spaciousness, always somewhere unspoiled to travel.

And Americans now, so many of them still on the move or at least fantasizing a move to a last big strike, are still attracted to traveling music and the dauntless loners who create it. Kris Kristofferson, for instance, and Bob Dylan, Johnny Cash, Charlie Rich.

These present-day songsters are seen as perhaps the last of the frontiersmen, needing no college degrees or professional licenses to reap large rewards as they roam the land, riding their guitars. If in an age of corporate envelopment, they keep alive the dream of the self-made American whose success comes not from "selling out" but just from being himself.

And there are other kinds of dreams. Black music, for instance, was eventually to color all popular sounds, even white country. In the "cry" of Charlie Rich's voice are echoes of the black work and religious songs he heard as a white boy in a small Arkansas farming town. But the foundations of black music are obviously built on centuries-long experiences largely unknown to other Americans. So viscerally unknown still that the televising of Alex Haley's "Roots" was a shock to millions of his fellow white citizens.

From the beginning of slavery here, black music was nothing less than a way of psychic survival. Field hollers were used to send messages; religious songs both shared the spirit and, in code, prophesied freedom. And the blues, as novelist Ralph Ellison has pointed out, were "one of the techniques through which Negroes have survived and kept their courage."

The blues were not only about hard, shattering times but were also ironic, difiant, proud. There was triumph in the blues, with heroes who had gone so far down they had nowhere to go but up. And up they came.

It is no wonder that the blues have never lost their strength, having been tested so much. And so the textures of the blues continue to pervade the "soul" music that now reaches huge numbers of white as well as black listeners.

More showy than classic blues, rhythmically driving, and mixed with gospel, "soul music" distills the black urban experience while also projecting young dreams of love and power. From Aretha Franklin to Stevie Wonder, both soul "superstars," black music still propels a directness of emotional force that no other American musical language has yet equalled.

Although blues recordings and performances were once limited to black communities, except for a few white aficionados, since the 1950s the blues and other black music have "crossed over" to all other popular audiences. Accordingly, the Top 40 lists are not only throughly integrated buy also contain records by white singers and musicians who are heavily influenced by black sounds.

In fact, there is not a single white rock band unaffected by the blues. Rock music began in the early 1950s as a white version of what was then called black "rhythm and blues." As white and black strains merged more completely than ever before in American popular music, ecumenicism became the rule.

In the 1960s, rock - mirroring the "counter-culture's" impatience with restrictions and categories - fused country cadences, jazz, blues, and various styles of pop music, from ballads to simple "good time" songs. Significantly, the most widely influential figure in the history of American rock, Elvis Presley, was himself stylistically an amalgam of what used to be heard as opposites - white country music and what he called "the real lowdown" black Mississippi blue singers.

Ond of the key reasons so many of the young have been drawn to rock has been its seemingly egalitarian nature. That is, in previous generations, it was generally felt that the making of popular music was limited to such highly skilled and sophisticated specialists as George Gershwin and Cole Porter. Even the singers, from Bing Crosby to Frank Sinatra, with their difficult big-band experience and coolly urbane manner, appeared to belong to a distant aristocracy.

Rock on the other hand, has given status to thousands of singers and instrumentalists who look and act very much like their fans; who write their own songs, and who, in many cases, have skills not too far removed from those of a dedicated amateur.

Reviewing such a rock combo, Big Brother and the Holding Company" - the group that featured white blues singer Janis Joplin - a counterculture critic wrote in the 1960s, "It's probably the secret dream of every kid every where to just do things they dig doing and be rewarded for it. America - as one America, the land where dreams come true, could - is making the dream come true for Big Brother."

And so, from the 1960s to the present, more of the young have been enthusiastically immersed in popular music than at any other period of our history. It is after all, their music.

Unlike the popular songs of earlier decades and centuries, rock is not primarily directed at grown-ups. It's about freedom from grown-ups; freedom to leap right into the middle of experience without having to lay back for fear of what some parent or teacher may think.

Elvis Presley did indeed succeed Porter and Gershwin. And in turn, he was at least partially dislodged by a more outspoken rebel, Bob Dylan, who in the 1960s, spoke for and to a whole generation of listeners who were, like him, antiwar and anti-all-establishments.

In the 1970s, and beyond, more lone stars in their early 20s will inevitably continue to speak to the dreams and nightmares of each new generation. There still remains, however, ample popular music for new and even for older adults. They still listen to the musical survivors of the 1950s and 1960s; and as James Talley says, they listen to remember the values of their quicksilver youth, as contrasted, if there is a contrast, with their values now.

Popular music always speaks, among other thing, of dreams - which change with the times.