In Leningrad the show was so popular that in its final days, the Hermitage Museum extended the visiting hours until 9 p.m., and still people lined up down the block to see 40 paintings from Washington's National Gallery of Art.

Today the show of French Impressionist masterpieces came to Moscow -- the first time in more than six years that an American exhibit has opened in the Soviet capital. J. Carter Brown, director of the National Gallery, was here to mark the occasion, which he hailed as "only the beginning."

"These glorious works of art are an opportunity to transcend the language barrier and all sorts of other barriers as well," he told a select crowd of invited guests at the Pushkin Museum.

The French Impressionist show, featuring works by Manet, Monet, Degas, Renoir and others, opened in Leningrad last month to help kick off the latest round in U.S.-Soviet cultural exchanges, which came into being with the signing in Geneva last November of a cultural agreement.

The National Gallery exhibit is only one of several events that have begun to fill up the bicultural dance card: an American musical, "Rag Dolly," came here in January, and next month pianist Vladimir Horowitz will give two performances here -- his first visit to his native country since he left it 61 years ago. An exchange of works by 19th-century Russian and American artists is in the offing. Leningrad's Kirov Ballet is bound for Wolf Trap, and on May 1, an exhibit of French Impressionist paintings from the Pushkin opens at the National Gallery before moving on to Los Angeles and New York.

Because this is Moscow, center of a highly centralized state, home of the Soviet government, the state media and the foreign press corps, today's opening was treated as a major event, with a press conference in the morning and an official ceremony in the afternoon, attended by the first deputy minister of culture.

American industrialist Armand Hammer, whose collection of masterpieces opens next week in Leningrad, attended the press conference, since he has financed the transportation of the U.S. exhibit here and will do the same for the Soviet exhibit that is going to the United States.

At both ceremonies there was much talk of the "spirit of Geneva," of a "first step" in U.S.-Soviet cultural exchanges, of art as the bridge to understanding, of the significance of the exhibit as a "gesture of trust."

Cultural exchanges between the two superpowers were suspended in 1980, after the Soviet invasion of Afghanistan and the lapsing of an earlier cultural agreement.

Since then, there have been occasional appearances here of American artists and works of art, but none with official backing. For Soviet audiences, the suspension of exchanges meant the end of an era that had brought them 100 masterpieces from the Metropolitan Museum in New York as well as exhibits of Peruvian gold, American modern art and other treasures from U.S. museums -- all fondly and vividly remembered.

So today, as soon as the speeches were over, people eagerly got in line to see the pictures -- hung on three walls of a single, stark room, with Edouard Manet's "Gare St. Lazare" in a place of honor.

This picture and Manet's "Dead Toreador" had been particularly sought by the Soviets.

Irina Antonova, who for 25 years has presided as director of the Pushkin, was also highly interested in works by Berthe Morisot, Fre'de'ric Bazille and Georges Seurat, whose works are not represented in the Soviet Union.

Brown, here for a one-day visit, said the decision to use French Impressionism as the first bridge for U.S.-Soviet exchanges of artworks started three years ago, when he saw a catalogue of a Soviet exhibit then showing in Switzerland.

Brown said he was so impressed by the Soviet exhibit that he decided to make a bid for it -- even in the absence of a U.S.-Soviet cultural agreement.

"We were quite far along in the process when it collapsed, and I can tell you the day it failed. It was the day the Korean airliner was shot down. After that it was as dead as a doornail," he recalled.

But the idea was in the pipeline -- the transparencies for the catalogue had even been ordered -- for the day when U.S.-Soviet relations improved, as they did last November at the Geneva meeting between Soviet leader Mikhail Gorbachev and President Reagan.

Soon after Geneva, some of the National Gallery's most famous and beloved Impressionist works became available for travel, as space at the gallery was taken up by visiting exhibitions, Brown said.

"If ever there was a time to lend these," said Brown, looking at the roomful of masterpieces, "this was the time." He said Soviet cultural officials were quick to seize the opportunity.

There has been criticism about inaugurating an era of Soviet and American cultural exchanges with French masterpieces, but Brown dismissed it.

"It is a subject everybody loves, and these are pictures which will fascinate the connoisseur," he said. "It was a wonderful opportunity."

Or as one visiting cultural figure put it, "When you want to launch a new orchestra, what do you start with? Stockhausen? No, you give people Strauss waltzes. Is there is anybody anywhere who doesn't love Impressionists?"