NEW YORK, SEPT. 2 -- Vincent van Gogh's spectacular "Irises," painted in 1889 during the first week of his voluntary stay at the Asylum of Saint-Paul-de-Mausole in Saint-Remy, will be auctioned here Nov. 11 at Sotheby's for a price that is expected to exceed $20 million.

John L. Marion, chairman of Sotheby's North America, said today that the painting will be "the most important work of art to be sold in America."

The work, which was a highlight of the Metropolitan Museum of Art's recent exhibition "Van Gogh in Saint-Remy and Auvers," comes to market in a year that has been marked by spectacular auction prices for van Goghs. "Sunflowers" sold for a world-record $39.9 million at Christie's in London last March, and another van Gogh, "Le Pont de Trinquetaille," went for $20.24 million at the same house in June. "Irises" is expected to go for something between those two prices, according to Marion,. The painting belonged to the late Joan Whitney Payson, an art collector and owner of the New York Mets, who bequeathed it to her son John Whitney Payson. Since 1977 the picture has been a part of the Joan Whitney Payson Gallery of Art at Westbrook College in Portland, Maine.

The painting was unveiled today at a Sotheby's press conference. Under tight security, two white-gloved porters carried in the lushly colored 28-by-31 3/4-inch painting, framed in surprisingly stark dark wood, and hung it behind the lectern at the press conference.

John Whitney Payson was on hand with members of his family to explain that the picture was being sold because of "the recent and unprecedented {upward} spiral in art prices." "Irises" is one of 28 works in the Joan Payson Gallery, and part of the proceeds from its sale will go to cover the expenses of maintaining the other 27. Because of the staggering insurance costs for van Goghs, the work has been kept out of sight recently in a secure storage room at the gallery, and the price of "in-transit insurance," required for transporting valuable artworks, makes it out of the question to lend the work to another institution. "The solution to these problems," explained Payson, "was the decision to sell a work of art."

The painting is brushed with history. "Irises," painted less than a year before van Gogh took his life, was one of 11 paintings sent by the artist to his brother Theo in Paris, and of those, "Starry Night" (now in the collection of the Museum of Modern Art) and "Irises" were chosen by Theo to be exhibited at the famous "Salon des Inde'pendants" show in Paris.

As part of Sotheby's presale promotion, the picture will travel to Osaka, Tokyo and London before its public viewing at the auction house in New York. Japanese bidders are expected to be strong contenders at the auction; the yen's strength is increasing and interest in art is high in Japan. This year's record price for van Gogh's "Sunflowers" was paid by a Japanese insurance company.

David Nash, director of Sotheby's fine arts division and an expert in impressionist works, said "Irises" is strongly influenced by Japanese woodblock prints, "in particular, Hokusai's 'Irises,' " a series of works completed in the 1820s and avidly collected by van Gogh and his contemporaries.

Of the van Gogh "Irises," Nash said, "It's the finest painting Sotheby's has sold since I started here 25 years ago." Over the summer Nash visited the still-functioning asylum in Saint-Remy and attests that the irises are still there in the garden, just as van Gogh painted them.

John Payson also announced that proceeds from the sale would be used to establish the Joan Whitney and Charles Shipman Payson Charitable Foundation, which will be aimed "primarily at funding Maine charities, with a special focus on the arts."