Washington's museums have been given a chance to buy what may be the world's finest private collection of American minimalist, conceptual and environmental art, said to be worth $15 million.

The owner, Count Giuseppe Panza di Biumo of Milan, has met with the directors of the National Museum of American Art, the Corcoran and the Hirshhorn, who describe their talks as "general," though all have expressed interest if funds and space are available.

Last February, Panza sold the earliest works in his collection -- 80 Abstract Expressionist and Pop Art paintings -- to the new Museum of Contemporary Art in Los Angeles (MOCA) for $11 million.

This week, he offered 500 more works to museum directors here, including examples by Bruce Nauman, Robert Ryman, Sol Lewitt, Robert Mangold, Brice Marden, Robert Morris, Joseph Kosuth, James Turrell and most other major artists of the American avant-garde in the 1960s and early 1970s. About 100 of these works have also been offered to MOCA.

Referring to the lack of advanced American art of the '60s and '70s in public collections here, Panza said, "They certainly need it."

They'll also have to pay for it. After 10 frustrating years of trying to give away the approximately 600 American avant-garde works he acquired between 1955 and 1975 -- first to various cities in Italy, then in Switzerland and Germany -- Panza is now trying to sell them.

"I am no more young," said the 61-year-old count. "I want to see my collection in a museum before my death."

The works acquired by MOCA in February included seven paintings by Mark Rothko, 11 by Robert Rauschenberg and other major works by Franz Kline, Claes Oldenburg, Roy Lichtenstein and George Segal. Panza says he bought them in the 1950s for a total of $300,000.

Now a member of the board of trustees of MOCA, Panza would also like to see part of his collection in Washington: "After all, it is the nation's capital," he says.

Space may be a problem. Panza wants to sell the collection in "meaningful units" of 60 works or more. Each unit would require roughly 30,000 square feet of space -- more than that occupied by any single exhibition to date in the National Gallery East Building.

The new director of the Hirshhorn, James Demetrion, was noncommittal. "I just started here yesterday, and we still have 6,000 objects coming in from Hirshhorn's bequest. But Panza's is a strong collection -- one of the strongest collections of American art of the '70s anywhere in the world -- and any museum that collects contemporary American art would be delighted to have selected examples in its collection."

Demetrion described their discussions by saying, "Panza just wanted to point out what his situation was, and that the proposals and hopes he had for keeping the collection in Italy aren't going to work out. Consequently, he's looking for other places. We'd be happy to have it, though it would be important to make selections."

Said Corcoran Director Michael Botwinick, who has visited Panza's collection in Italy, "It's one of the really great collections of American art of the '60s and '70s. But the real issue is whether there are the private resources to buy a piece of it. He's selling it in groups, and there are sections that have an integrity of their own. He hopes, I speculate, that if he offers major institutions favorable terms, he can keep some of those artistically meaningful sections intact. If there is a group of donors out there who would buy a hunk of Panza's collection, it would be a great thing not just for the Corcoran, but for the city, which is short on this art."

The Corcoran's new curator of contemporary art, Ted Rifkin, called Panza "one of the more visionary collectors in the western world."

Panza has had hopes of housing his collection in one museum. So far, the closest he has come is the renovated stable of his 18th-century country house in Varese, outside Milan, where several commissioned, site-specific sculptures by Dan Flavin, Sol Lewitt, Robert Irwin, Bruce Nauman and others are installed in a series of small rooms. The stable at Varese has become a mecca for avant-garde artists and art lovers.

Panza is still involved in his family business -- real estate and commercial alcohol. But he has offered his collection in Los Angeles, and will go to Philadelphia and New York from here. When he returns to Milan, he will have further discussions with museum officials from Detroit and San Diego, as well as from Paris, Frankfurt, Hamburg, Edinburgh and Lugano, Switzerland.

"I could just sell it all at auction for a good deal more money, but that's not what I want," Panza said.

Panza is also seeking a cooperative arrangement with some American university that might set up and support a study center at Varese, on the model of Bernard Berenson's former home, i Tatti, outside Florence. Panza calls this American art of the mid-20th century "revolutionary -- as important in transforming the language of art as was the Italian Renaissance."

Panza's problem is not unique to large-scale art collectors. He spoke wistfully of how "lucky" Joseph H. Hirshhorn was to have found a home for his collection in "that beautiful building on the Mall." Baron Hans-Heinrich Thyssen-Bornemisza of Lugano has also spent considerable time seeking a proper home for his 20th-century holdings. He has decided to build his own museum of modern art in Lugano.

Asked why he did not do likewise, Panza said, "He is a baron and a billionaire. I am only a small millionaire -- in Italian lire."