Claes Oldenburg is a sculptor whose ideas take some getting used to. Imagine the Washington Monument, for instance, replaced by a giant scissors. Or London's Thames River outfitted with a colossal brass toilet float that rises and falls with the tides. Or huge windshield wipers sawing through the air above Grant Park in Chicago. Why not a pair of gleaming black bowling balls two stories high on New York's Park Avenue?

The proposals are not as nutty as they seem. At Yale, students in Morse College now gaze out at Oldenburg's 24-foot-high Lipstick mounted on caterpillar tracks. (Its message is make love, not war.) In Arnhem, Holland, a park is graced by his 40-foot-high, gleaming aluminum shovel, nestled in a giant mound of earth. One wealthy Connecticut couple displays his two-ton lead baseball mitt on their lawn, and the elegant new Hirshhorn Museum in Washington has acquired Oldenburg's massive Geometric Mouse.

The art world has succumbed to the visionary gigantomania that typifies the work of Claes Oldenburg. Critics now rate him among the most original sculptors in the world. Collectors pay up to $60,000 for his pieces. His third major retrospective is currently on display in Minneapolis and will travel on to Denver, Seattle, New Orleans and Toronto.

"I'm a magician," says the 46-year-old Oldenburg, thus defining his artistic role as one of bringing a lifelike quality to inanimate objects. He is deadly earnest about his blown-up metaphors of Pop commercial culture. "Why should a monument commemorate something that happened 100 years ago? It should reflect what's going on today." Left-wing philosopher Herbert Marcuse, for one, takes Oldenburg's images seriously indeed. Says Marcuse, "This kind of satire can kill. But these works can be a bloodless means to achieve radical change."

Born in Sweden, Claes (pronounced Kloss) and his brother Richard, now the director of New York's Museum of Modern Art, were brought to Chicago in 1936 by their diplomat parents. Claes showed only moderate interest in art until his graduation from Yale, when after a short stint as a cub reporter, he enrolled in the Chicago Art Institute.

In the late '50s he made his way to New York, where he got a job as art librarian at Cooper Union. "Things were dull then," Oldenburg recalls. "Jackson Pollock had died. Abstract expressionism was on the way out. There was a lot of confusion about what was going to happen. I wanted to give art some life."

So he did, and "all hell broke loose," he recalls. He started with the first of his many "happenings," selling such "art objects" as plastic ham-and-cheese sandwiches for $279.98. Before long his soft sculptures—the droopy telephones, clothes hangers and electric fans (which were sewn out of vinyl by his wife)—propelled him into the "Big Three of Pop Art" along with Roy Lichtenstein and Andy Warhol.

The sewing machine is now stilled (Oldenburg was divorced in 1970) and Pop art has passed, but Oldenburg continues to flourish. He lives in a cavernous five-story warehouse in Lower Manhattan where he works with an intensity that belies the wit and irony of his drawings and sculpture. Ideas, each more bizarre than the last, come to him by the hundreds. He scours magazines daily for more, filling an entire bookcase in his studio with notebooks of sketches and clippings. Some of his ideas will soon show up as public monuments. He is planning one for Chicago, and others are under consideration by Philadelphia, Houston and Los Angeles.

Oldenburg no longer creates sculptures out of limp vinyl, but out of metal and hard plastic. His new Alphabet/Good Humor, a sculpture that looks like an ice cream stick decorated with letters, is fabricated of bronze and fiberglass. He spends increasing amounts of time at the iron foundry he uses in North Haven, Conn. But the spirit of fun and fantasy continues to guide his work. "What I do is always a performance, a happening. Every time I install one of my monuments," Oldenburg says, "it is a kind of theater."