An internationally acclaimed millionaire artist has come to the aid of an Arlington woman in a legal fight with her condominium association.

Friedensreich Hundertwasser -- a renowned Austrian painter, printmaker and eccentric who spends much of the year on a sailboat anchored off New Zealand -- first learned of the plight of Mireille Alberti through a newspaper clipping sent to him by his Washington agent. The story described Alberti's fight to keep the bay window she installed in her Laurel Green home 15 months ago, contrary to the bylaws of the condominium. Her co-owners sued, and the court ruled that the window has to go.

Hundertwasser leapt to Alberti's defense in a four-page letter, which said, in part: "Man must have the freedon to lean out of his window and change his outside wall as far as his arm can reach, so that one can see from far away, and say: There lives a man, a free man who distinguishes himself from the imprisoned people! To put people or animals into prefabricated dwellings without possibility to change them to their real needs is equivalent to putting beings into prison, into breeding boxes or into concentration camps."

The letter was transmitted through Hundertwasser's American dealer, Manfred Baumgartner of Washington. Hundertwasser, a reclusive ascetic and avid maker of manifestoes, has offered money, lawyers, "all possible means at my disposal."

"I'm amazed! I never heard of him," says Alberti, a French immigrant who was taken to court early last year by the Laurel Green Condominium Association for replacing a sliding-glass door with what has been called a "Dutch Colonial" bay window. The condo's bylaws state that such permission must be granted before changes can be made.

After 15 months of battling over the case, combined legal costs for the opposing parties have reached $17,000, and an Arlington judge has found that if they cannot settle out of court by Monday, the window must be restored to its original appearance, and Alberti must pay $4,000 -- half the association's court costs.

Hundertwasser, 56, offered Alberti the $4,000 and more, but she has refused. "I'm proud and I'm stubborn," says Alberti, whose attorneys say that they may have to ask for a continuation of the case because "it isn't easy to find contractors at this time of the year."

Meanwhile, the condo association president, Jeanne Salvia, is planning a party to celebrate the association's victory tomorrow at 3 p.m. Alberti, who was not invitted, says she'll celebrate by giving a party for Hundertwasser when he comes to town.

That could be soon. The environment-conscious artist also has offered aid to another Washingtonian, Ralph Nader, by donating 5,000 original Hundertwasser posters to be put on sale at $40 each to benefit Nader's Critical Mass Energy Project. "I completely support you in your blessed activity," the artist wrote to Nader.

"We're delighted," says energy project director Richard Pollock. "He's been an advocate for the environment for years, and this is an unusual project that joins two highly unusual people, as well as politics and art."

Though Hundertwasser is less well known in America than in Europe, his works are highly priced and prized throughout the world, and some early posters trade in four figures. Out of his admiration for President Senghor of Senegal, he designed three stamps for that country. He also has been pushing for legislation in Austria which would guarantee what he calls fensterrech -- window rights.

In the letter to Alberti he explained: "Nobody contests today your right to choose your clothing, your right to travel and food and your right of opinion in the free world. Why is the right to your own window still a problem?"

On the subject of Hundertwasser's activities here, Alberti quoted a French proverb: "Rich people and crazy people have one thing in common. They do what they want."