If mellow had a motor pool, it would be roller skates, much like the ones gaining speed under me on the bike path in Rock Creek Park. They have precision bearings and eight urethane skateboard wheels, a technological feat which has wrenched all of California out of hot tubs and into skates, if word-of-mouth and media are to be believed-Linda Ronstadt, Jerry Brown, Mork and Mindy, Dustin Hoffman, Lily Tomlin. . .

I have Rock Creek to myself, floating-not grinding like the old metal-wheel side-walk clamp-ons-under a jet-etched blue sky, past the Pierce Mill waterfall, a stray crocus or two, as in those dreams where you're flying and it's so easy.

"It's unbelievable. Our sales are double what they were a year ago. We're four weeks behind on deliveries," says Harry Ball, president of the Sure-Grip Skate Co. in Los Angeles.

"People wait in line for two hours to rent skates on weekends," says Judy Lynn, who gave up teaching yoga to open a skate rental concession last spring in New York's Central Park."I think it's going to cover the earth and save the human race."

Playboy ran a photograph of a woman naked save for roller skates. Linda Ronstadt wears them on the cover of her latest album. RollerSkating magazine covers roller beauty contests, roller slaloms, roller speedskating. The Pan American games will feature roller-skating dance, art and speed contests this year. A.D.C. teacher has been rolling on the picket line in front of Harriet Tubman Elementary School. Around 2,000 people have entered a roller-skating marathon in Long Beach, Calif., with an expected winning time for the 26-mile race of an hour and 45 minutes. Macy's features a roller-disco boutique, tutus and satin in astonishing orange, electric fuchsia. . .

"It's got beautiful demographics, just beautiful," says Sure-Grip's general manager, John Poe. "Skateboarding was all male, 10 to 15. This is everybody, 5 to 70, with a big bulge in females 40 to 45-that group has never had an athletic program."

It's got a book, "Keep on Rollin'," by Sharon Borstin, which promises, among other things, that skating eases menstrual cramps and strenghthens vaginal muscles.

It's got touring shows of roler-disco performers, and its very own doctor, a California podiatrist named Allen Selner who says roller-skating burns 360 calories an hour, and is nearly unquie in toning up the avductor and vastus lateralis muscles of the thigh, thus shrinking the dread cellulite and "chaps."

"We've got the skates" shouts Sandy Dezen in the SweetSkates rental booth at the L.A. Cafe, on 18th Street NW. The music traphammers down from the brick walls, two mirror balls smear lozenges of light across the dance floor where nobody quite knows what to do with this, how-you-say, roller disco that's just arriving here-while New York, where it started, is bracing for whole 20,000-square-foot roller-disco only ballrooms this spring.

"Roller disco is here to stay," says Cafe manager Nestor Hernandez, who's wcheduled it for Tuesday nights.

"Horrible, man, just horrible," says a man with a 220-volt Afro, and a pair of skates which have him hanging onto the walls not even thinking about dancing in these things.

In fact, the best anyone manages to do is circle the tiny floor, as if this were a rink, rather than a disco, until some heavies move onto the floor-you can tell because they're wearing their own skates. And suddenly it's like dance that's pure float out there-glides, spins, eagle spreads with the feet parallel, heel-to-heel, like dancing without your feet ever having to come down, in fact.

"I flew in from New York just for tonight," says Hap Beasley, who's helping a friend open a roller disco on 55th Street.Besley's grace triumphs over the mundanity of straight-leg Levi's, even the pot-belly underneath his T-shirt-he scissors, he cross-steps, he leans his bearded head back and boogies, all by himself, partners seeming merely anadded fillip, a chance for even more elaborate work.

And is it just the fad of it all, or do people in here actually look sexier, wearing skates, even while they're resting? The satin skating shorts on one woman might have something to do with it. But as the floor fills with more people who know what they're doing, everyone else at the L.A. Cafe, disco's foot soldiers starts to look clumsy, ordinary-yes, pedestrian.

SweetSkates is two women: Dezen, and her partner, Sam Talbertt. They didn't empty bank accounts to rent skates in a disco, however. They think of Central Park, of Venice, Calif., and they want to get into Rock Creek, the Washington Monument grounds, Hains Point.

Dezen sold her 30-foot sloop and Talbertt is on unemployment. "We've got 56 pais of skates," says Dezen. "It was 57 last week but we ate one pair."

"We finally fot the parks people to let us skate on the bike paths. Now they won't let us set up a rental concession. They'll let you sell things, but you can't rent things," Sezen says.*tIf you take Washington's legion of joggers, and put them together with the fact that the area already has 13 rinks, a large potential emerges.

"We want to make this like skiing, a class sport," says Talbertt

Roller-skating? Roller rinks, in recent history, have ranked well below bowling alleys and pool halls as status nightspots, pulsing with images of sailors fighting on the sidewalks, men's rooms no one would enter without close air support.

The National Roller Rink, for instance, on Kalorama Street, has all the trappings including neon sign out fron which reads:

AMERI ON WEELS

But inside, ignore the walls that look like they used to be part of the Baltimore Harbor Tunnel, the sad old deserted organ pit, the sparse week-night crowd. The new roller-skating craze hasn't hit here yet, but the old one will do.

A hundred roller freaks are jamming around the floor at raceway speeds, legs twinkling in impossible leaning cross-steps, arcing through figure-eights, leaping, spinning, or merely cruising, hands in pockets in an extravagance of simplicity, all of it grace that pours in through the eyes to knead the brain like a cold-ceam massage. Soul on wheels! Mellow! In the land of the roller skaters, the man on foot is crippled.

Nothing could make that point clearer than the man who misses a jump, just now, in center rink, and falls. He falls not with arms flapping like an undecided duck, or scattering of limbs to the wind. No, up at kalorama one takes a spill by sprawling supine and extravagently akimbo, beaming a total-surrender smile at the revolving-mirror ball.

"Yeah, they all been coming up here for a thousand years, man," says George Dunmore, 17. "They do the spin, the snap, the eagle spread. Then they put their own style to it to look good."

"Freedom and joy," says Keith Mathis, who has just come off the floor, where he spends hours in slow, Apollonian glides through all the required figures of artistic skating.

Freedom, 360 calories an hour, out-door exercise, disco, celebrities, so many of them skating now in California that they're formed their own Skateaway Club. They rent the Sherman Square Roller Rink in Sherman Oaks, Calif., every Monday night so Cher and Richard Harris and Desi Arnaz Jr. and "just everbody" can skate in starry solitude, says Jeff Rosenberg, who started the whole thing three years ago May 23 on the concrete boardwalks of Venice, Calif., renting them to his friends.

"I started with 25 pairs. I have 1,000 pairs now," he says. And for all of us getting set for yet another California fad, it's nice to know it was no willful plan to leave us all behind. "It was just kind of an idea," Rosenberg says. "It wasn't, youknow, like a well-thought out plan."

Mellow!