Grinning his infectious grin, artist Robert Rauschenberg stepped upon the rubber tread of the inclined moving sidewalk and rose toward his mural out of the gloom of the underground garage. He had come to Children's Hospital for yesterday's unveiling of the $100,000 work he calls "Periwinkle Shaft."

Multiplied by the mirrors he'd installed on the walls above him, he rode into the light, a smiling apparition. His shirt was tan, his skin was tan, so were his wing-tip shoes. His arched, stuffed purple gamefish hung above his head like some loony seaside moon.

His complex mirrored mural, with its many parts, its horses and lizards, red lights and fun-house mirrors, was, he said, "arranged to be fast entertainment for people in stress. It's the first time I've done anything for a mobile audience. I think of it as a conservative environmental piece conceived to add confusion." It may not be his finest work but it does wonders with the space.

"There is no symbolism in 'Periwinkle Shaft,'" he said. But, of course, there is.

"The shaft part," he said, "is a double pun." Shaft refers to both the tall, dark space selected for his mural -- and to what he thought he'd been given when he first saw the space. "You should have seen it," he said. "The moving sidewalk squeaked and there was no light. It felt like the subway platform at 42nd Street. All the miracles were upstairs."

The periwinkle is a kind of shellfish and also a flower that grows in profusion around his Captiva Island home on Florida's Gulf Coast, where he makes art by the sea. "I read somewhere that they were examining that flower here at Children's Hospital as a cure for cancer. Cancer and wildflowers -- that's hard-core Romanticism. I added a purple fish."

Rauschenberg has been rich and poor, an art star and a failure, a joker and a prophet, and he is among the most inventive of all living artists. At one time or another, his career has brushed, or, perhaps crashed into, those of Josef Albers and John Cage, Duchamp and deKooning. He worked with Jasper Johns and danced with Merce Cunningham. Countless are the artists his influence has touched. In retrospect he seems completely inescapable, and his work runs like a thread through the complex labyrinth that is post war U.S. art.

He was born in 1925 in Port Arthur, Tex., Janis Joplin's hometown. His given name was Melvin, but he gave it up in 1947. Robert sounded better. In between his names, the R sounds and the Bs, one can hear the echo of those odd juxtapositions, those open-ended rhymes that characterize his art.

What is most confusing in his art is its mix of opposites -- delicate and tough, sophisticated and raw, metallic and silky-soft, the action painter's gesture and the hard-edge line. A scavenger of genius, he tugs things out of real life -- stuffed goats and fish and chickens, pillows, cardboard boxes, rubber tires, curtains, quilts -- and glues them to his pictures. His imagery suggests mind-boggling variety.

There are Big Macs and bandannas, sailboats and seas and puns on Albers' paintings (Albers taught him at Black Mountain), and a big red apple -- a treat for the teacher? -- in "Periwinkle Shaft." His work might seem at first abstract, arbitrary, plotless, closed to interpretation. But look at it a while, and that confusion fades.

Children are fond of motorcycles, fun houses, hamburgers and animals; of tigers, horses, silly geese and scary lizards -- and all these are in "Periwinkle Shaft." One early work of Rauschenberg's, a combine titled "Odalisk," seemed very strange when new: It included, in addition to many images of bosomy beauties, one large white stuffed rooster. But why not suggest the harem through the introduction of that proudly male bird?

A small retrospective of Rauschenberg's work of the 1970s goes on view this weekend at the Baltimore Museum of Art. That little show -- arranged by Brenda Richardson -- with its "Hoarfrosts," "Jammers," "Combines" and cardboard "cardbirds," is even more impressive than "Periwinkle Shaft."

In one piece on view there, real broken orange life jackets seem to be afloat on a sea of flame. The images beside them -- of tall ships, crashing surf and fishermen at their nets -- underline the sense of sea, as those silk-screened pictures of flaming oil drilling platforms, working firemen and fireworks, add fuel to the fire. Rauschenberg, though famous for his freedom and spontaneity, makes art that can be read.

Many recent Rauschenbergs recall those of the past. That stuffed purple fish of "Periwinkle Shaft" belongs to the same zoo as that white stuffed rooster and his famous goat. Certain other motifs -- the parachute, the veil, the pillow and the tire -- recur like theme songs.

Rauschenberg is rich now. Half of the $100,000 Children's Hospital commission came as a matching grant from the National Endowment for the Arts; a quarter came from Mr. and Mrs. Leo A. Daly III (he designed the hospital); and the rest was given by an anonymous donor. His Baltimore museum show calls attention to another mural -- this one a $250,000 commission -- that soon will be unveiled in the new Equitable Bank Center nearby.

But when Rauschenberg met Jasper Johns in the 1950s, the two painters were so poor that Johns once fainted from hunger. Last week one of Johns' flag paintings was sold for $1 million to the Whitney Museum of Art. It had cost $900 new, plus a $15 delivery fee. Rauschenberg's best works are not yet in the $1 million range, but they're getting close.

"Jasper said money doesn't have anytrhing to do with art," Rauschenberg said yesterday. "I haven't agreed with Jasper for 25 years, but I agree with that. When I first became successful, success wouldn't give me a break. It was a kind of irritation, an interruption in the line between, you know, getting up in the morning and going to make art."

However, Rauschenberg added, "there is a picture of a dollar bill in Periwinkle Shaft.'"