There was a time, before our Manifest Destiny landed us in L.A., when the cowboy was the real symbol of America.

Dogged and tireless, he was the immigrant pioneer idealized.Like his animals, he had more instinct than intellect -- more of a spirit than a soul. He adhered to an awful, disinterested justice and a necessary asceticism.

He rode the plains of our imagination, aloof and inviolate, until America grew tired of ascetics and transformed the "Protestant ethic" into the golden rule of commercialism. Suddenly the cowboy was peddling his integrity instead of living it.

Today he smokes Marlboros or drinks Miller, or is part of the plastic machismo in big-city bars. His ragged leather seams have become the Cowgirls' vinyl fringe. The word "outlaw" is just an excuse to mix '60s indulgence with '50s country music.

Yet, like all the symbols with the power to move us, the cowboy still exists -- in folk music, the last refuge of undecorated emotion. And last night, that symbol's final troubadours, the Sons of the Pioneers, figuratively placed that music in trust for the future in a concert at the Smithsonian's Baird Auditorium.

"I've never been declared a 'national treasure' before," says Rusty Richards. "I'm thinking of adding 'N.T.' to my name."

The Sons of the Pioneers have existed continuously since 1934, since their founding (as a trio) by Bob Nolan, Tim Spencer and a Cincinnati kid named Leonard Slye -- better known as Roy Rogers. Since that time there have been 16 Sons, at various times including Pat Brady (Rogers' jeep-riding TV sidekick) and "Gunsmoke's" Festus, Ken Curtis. Their current leader, Dale Warren, has been a member since Curtis departed in 1952.

They've recorded a half-dozen or so albums and sung in more than 100 movies. They have their own newsletter, "The Pioneer News," founded only a year ago. They play rodeos and Reno, county fairs and colleges, "Dinah" and Johnny Carson -- altogether 225 dates a year. They're busier than they've ever been, but they don't think it's because of some passing nostalgia. "We always talk about the past members, the present members and, hopefully, the future members," says Richards.

The Sons of the Pioneers -- Warren, Richards, Billy Liebert, Roy Lanham and Rome Johnson -- don't even like to think of themselves as "maintaining a tradition" in the face of progress.

"We're innovating," insists Warren. "We don't just play 'Tumbling Tumbleweeds' all the time -- we play all kinds of music. We do some stuff Willie Nelson sings, and Bill plays 'St. Louis Blues' on the accordion."

And in any case, if there's any looking back about it, it's the other way around -- Nelson to the Sons.

"'Blue Eyes Cryin' in the Rain' -- we recorded that back in 1945," says Warren. "And Marty Robbins' 'Among My Souvenirs' -- we did that about '45 or '46."

In the best cowboy tradition, the group members have to talk around rather than articulate their existential dilemma: how to grow artistically while continuing to protect that portion of America's musical heritage they represent. The most appropriate metaphor for that dilemma seems to be California itself, where the wilderness still exists but you can't see it for the interstates.

"(The cowboy's) way of life is not dead," says Richards, who raises and trains Arabian horses for his Orange County, Calif., ranch and three others. His colleagues agree, murmuring that California for all its famous smog, is still the No. 1 state in agriculture and that the population of the whole state of Montana is only 200,000 (it's actually closer to 750,000, but the point is valid).

But it is Richards who finally sums up their raison d'etre, in a story that even he doesn't see for the perfect legend that it is. He is talking about his son and driving through California past an impenetrable canyon.

"It happened that I had been riding in there a couple of years back, and when my son said, 'What's behind that canyon?' I said, 'It's beautiful. You better hope there is some kind of development around here if you ever want to see that wilderness, because right now you couldn't even get into it.'

"And he said, 'I don't care if I never see it; I just want to know it's there.'"