In the first Soviet-American cultural exchange arranged under an accord signed at the Geneva summit, the National Gallery of Art and two major Soviet museums will swap exhibits of masterpieces by impressionist, postimpressionist and other painters, American industrialist Armand Hammer announced today.

Hammer, chief executive of Occidental Petroleum, completed plans for the exchange of paintings by such masters as Pablo Picasso, Claude Monet and Vincent van Gogh in meetings with Soviet officials this week.

Forty works by seven painters from Leningrad's Hermitage museum and Moscow's Pushkin Museum of Fine Arts will be exhibited at the National Gallery next May and June, Hammer said at a news conference. The exhibit also will be shown in the Frances and Armand Hammer Wing of the Los Angeles County Museum of Art.

"It is the greatest collection of impressionists and postimpressionists to ever leave the Soviet Union," Hammer said today. The American businessman has nurtured contacts with Soviet leaders for decades and pioneered trade between the two countries.

In Washington, John Wilmerding, deputy director of the National Gallery, said the paintings to be sent by the Soviets are of "world class," Washington Post staff writer Carla Hall reported. He added: "They are among the least seen of French paintings and the least traveled."

J. Carter Brown, director of the National Gallery of Art, called the Soviet exhibit "intelligently chosen. It has clusters of works of art by the most important artists -- Henri Matisse, van Gogh, Paul Gauguin, Paul Cezanne, Picasso -- instead of a smattering of a little bit of everyone."

He noted that two previous efforts to bring some of these paintings to the United States had failed because of political crises between the United States and the Soviet Union.

A preliminary list of paintings to be included in the Soviet show has nine of Gauguin's Tahitian scenes; six canvases from the Hermitage's collection of works by Matisse; eight landscapes, still lifes and portraits by Cezanne; three landscapes by Monet; three portraits by Pierre Auguste Renoir; three works by van Gogh, and eight canvases by Picasso encompassing his cubist work and examples of his later styles.

Among the best known are Matisse's "Red Room," which Brown said "knocks your eye out"; Picasso's "Portrait of Ambroise Vollard," and Monet's "Woman in a Garden."

Many of the paintings from the Hermitage were obtained by Russian collectors Ivan Morozov and Sergei Shchukin before the Soviet revolution.

"Those two collectors were in on the ground floor," Brown said. "They knew the artists, and they got in when the going was good."

In exchange, two collections from the United States will be shown in the Soviet Union in February and March.

Soviet museums will be loaned "The Armand Hammer Collection: Five Centuries of Masterpieces" and 40 impressionist and postimpressionist paintings from the National Gallery.

The Armand Hammer collection made its debut here after the 1972 summit meeting between president Richard M. Nixon and Soviet leader Leonid Brezhnev.

Hammer, an art collector, has been organizing the exchange for two years. It would not have been possible without the cultural agreement, he said.

Hall reported the following from Washington:

The exchange of paintings was arranged after Brown joined Hammer in requesting it from the Soviet government, both men said in interviews. Earlier efforts to bring an exhibition of paintings from the Soviet Union to Washington collapsed after the Soviet invasion of Afghanistan in 1979 and the shooting down of a South Korean airliner in 1983.

Brown said he first saw most of the works to be sent here at an exhibit in Lugano, Switzerland, at the private museum of Baron Hans Heinrich Thyssen-Bornemisza.

Brown said he proposed that the show be sent to Washington. The Soviets, he said, "were willing, but they needed a blessing from the American side, and of course there were still fairly chilly relations. The day that Ambassador Arthur Hartman and Secretary Shultz were going to discuss this, the Korean airliner was shot down. All these plans we'd made . . . were shot down too."

Hammer, speaking by telephone from London, where he had flown from Moscow, said he had a similar idea when he saw the baron's show.

"We thought it was so spectacular," Hammer said, "that the first chance I had to get to Moscow, I saw Mr. Pyotr Demichev the Soviet minister of culture and tried to get it for the U.S. He said he'd love to give it to me, but not until there was a cultural agreement. He promised me I'd have first crack at it when there was an agreement."

Hammer negotiated the 1973 American tour of Soviet-owned impressionist and postimpressionist works that came to several museums including the National Gallery.