VIENNA -- "The straight line is godless and immoral," Friedensreich Hundertwasser says with a straight face as he shows off the four-story museum he is building here to house his own works. The ground floor is uneven, and treading over its rippled surface, Austria's best known living painter lets loose another personal catch phrase: "Walking on a wavy floor is like a melody for the feet."

Hundertwasser, who first earned international prominence in the 1950s through vivid paintings in the spiral pattern that has become his trademark, sees himself as an architectural iconoclast. He made his debut as an architect in 1985 by designing a fanciful public housing project, now an established landmark and one of Vienna's biggest tourist attractions.

More than 2,000 visitors troop by daily to ogle its colorful patchwork facade, gilded onion domes, grass-covered rooftop and tree-sprouting windows. A gift shop trades profitably in Hundertwasser postcards, posters, calendars, books and scarves. A guest book overflows with tributes from around the globe: "So awesome! We need one in California"; "Magico!"; "Un chef d'oeuvre d'eccentricite'!"

Encouraged by this resounding popular triumph, Hundertwasser has embarked on a polemical crusade to transform his country's architectural landscape. In addition to the museum, opening early next year, he is covering a gargantuan trash incinerator with ceramic tiles and gilt enamel. This after he planted grass and trees atop an existing highway gas station, and similarly altered a traditional village church. A Hundertwasser-designed shopping center and kindergarten are in the works.

"Now that there has been a revolution in the Eastern Bloc countries, the liberation from architectural dictatorship has still to come and is long overdue," says the 61-year-old Hundertwasser. "People are longing for this liberation, to finally live in buildings which fit them, which fit the dreams and longings they have had since prehistoric times... . What I want to achieve concerns not only me, it concerns all mankind."

Utterances of this kind are nothing new for Hundertwasser. In 1968, he issued a manifesto deploring the sterile legacy of modern architecture, attributing much of the blame to the rigid purity of fellow Viennese Adolph Loos and declaring, "It is from Austria that the architectural crime was released into the world. Therefore reparations must be proclaimed from this place."

His hopes for a harmonious, ecologically sound architecture have carried over into political activism. He once delivered a lecture in the nude as part of a protest against inhumane buildings and has advocated giving up flush toilets in favor of composting tubs to ease waste disposal. Hundertwasser created posters for Ralph Nader's Critical Mass Energy Project and traveled to Washington in 1980 to plant trees at Judiciary Square in a promotion of ecological awareness. He has designed alternative flags for Australia and New Zealand, where he lives part of each year, as well as postage stamps for Austria and Senegal.

Last year Hundertwasser led a popular but unsuccessful battle against plans by the Austrian Ministry of Transport to convert the country's white-on-black automobile license plates to black-on-white, judged optically superior by officialdom. He collected 300,000 signatures on a petition against the new tags, which he contended went "against the Austrian soul" and were disquietingly similar to those of neighboring Germany.

But his latest projects are meeting with increasing opposition from critics who allege that he is merely a cosmetician for Austria's environmental problems. "Typical of all Hundertwasser's building projects is that they involve structural and/or conceptual deception," declared the Viennese newspaper Die Presse. The leader of Austria's environmentalist Greens Party derides Hundertwasser's style as "Compost-Modern."

The critics argue that Hundertwasser has become a prisoner of naive eco-architectural aspirations, churning out buildings cloaked in decorative kitsch whose structure and interior layout differ little from conventional construction.

"The results border on charlatanism," Greens leader Johannes Voggenhuber says. "And I state this with a certain bitterness. I used to see his position as something which could be defended, but what he now does has little to do with architecture or ecological thinking. With Hundertwasser, it's pure decoration through which an environmentally destructive society is beautified and camouflaged, but in reality things do not change."

Friedrich Achleitner, author of a three-volume guide to 20th-century Austrian architecture and professor at the Vienna Academy for Applied Arts, says Hundertwasser originally had a valid response to architectural formalism but is now "producing alibi buildings which distract from the real problems. In truth, this is hot air."

But Hundertwasser, who conducts a tour of his museum dressed in a coat of many colors and a floppy cap whose pattern recalls the hodgepodge exterior of his buildings, finds the critics out of line. "I'm attacked for overdoing things. I'm attacked because I transform industrial sites. I'm attacked because I have money. I'm attacked because my paintings bring money at public auction," he says. "What is that? I must excuse myself for the success I have? ... My popularity gets out of my hands, and people ask for books and more postcards and more posters and more buildings. It is the demand which makes things this way. You cannot stop the demand."

He says he agreed to undertake the $8.4 million transformation of the Spittelau trash incinerator, just outside of downtown Vienna, only at the insistence of the city's socialist mayor, Helmut Zilk. "First I refused to do it for one year, for environmental and ethical reasons. I thought, 'I don't want to be involved with something dangerous, since I fought against nuclear power plants.' But then I had to yield to the evidence that the public rubbish can't be transformed into healthy soil because it consists of poison -- iron, lead and heavy metals, dioxins and plastics."

Zilk convinced him of the safety of the plant, equipped with filters to block noxious emissions and a system that further purifies the exhaust with water. The resulting energy from the vast plant, whose exterior alteration will be complete next summer, heats much of the Austrian capital.

"But the real reason I did this is because up until now artists, architects, sculptors denied all responsibility for industrial sites. They're off limits," says Hundertwasser. "Artists only do museums, monuments, maybe housing, but even that is beneath our honor... . When you want to better your world you must start with the industrial sites, you must start with the incinerating plant, the gas stations. These are the buildings that pollute."

His redesigned gas station, set on the main highway between Vienna and Graz, was previously a dreary prefabricated rest stop. Now grass and trees grow from its roof. The sheet-metal walls have been pleasantly plastered over, and the cornices feature glazed columns and cheery ceramic knobs that give it the appearance of a miniature golf links for children.

"The highways are destroying the landscape," he explains, "and it's no use fighting this. What way would there be to fight against a gasoline station -- to bomb it, to blast it so that it would not be there? Another solution is of course don't use a car, use a bicycle or public transport, but this works only in a limited way. So I do it the other way, by making forests out of gas stations... . Then people slow down, they don't rush on the highway. They think, 'Oh, it's beautiful.' By some sort of magical transformation it becomes less and less a gasoline station and more and more a forest. Then I have killed the gasoline station."

Apparently impressed with this thinking, another leading gasoline company has commissioned Hundertwasser to design a station near the site of the 1995 Vienna World's Fair. The artist says his "humane" highway stops could become commonplace.

Hundertwasser's museum, the Kunsthaus Wien, located a few blocks away from his public housing project in Vienna's Third District, will seek to further present the case for his controversial approach to architecture. The painter is paying for half of the construction costs, with the other half coming from a culturally active Viennese bank. (Among the names on the museum's advisory board are Laughlin Phillips, director of the Phillips Collection; James Demetrion, director of the Hirshhorn; and William Lieberman, chairman of the 20th-century art collection of the Metropolitan Museum of Art.)

The exterior walls of the building, formerly an abandoned warehouse on the Danube Canal, have been covered in a checkerboard of black and white tile, set off-angle in revolt against what Hundertwasser calls modernism's "dictatorial" hard edges. The windows are of blue and copper glass, and there are special portals for vegetation, or "tree tenants," as Hundertwasser terms them. "They pay their rent by producing beauty, swallowing noise and dust, producing clean air. It's a symbol of how to bring nature back to the town."

On permanent view will be a retrospective exhibition of Hundertwasser's paintings, graphics, wood cuts, tapestries and architectural models, plus exhibits on his environmental ideas. "It is the duty of a painter to show things if he knows a way, and it's a way I believe can bring solutions," Hundertwasser says. "It would be irresponsible to paint for myself and use the money for cars, rich women, fur coats and all that. No, I like to invest what I get for my art into showing the way."