The galleries were filled with Gauguins and van Goghs, the air with talk of Monet's light and Matisse's flowers at last night's National Gallery of Art party in honor of the first major art exchange resulting from the cultural agreement signed at last year's U.S.-Soviet summit. But one other subject could not be avoided.

"As we celebrate this reopening of cultural relations between our two great countries, our hearts tonight go to those in the Ukraine," industrialist and art collector Armand Hammer told about 120 dinner guests, referring to this week's nuclear accident near Kiev. "It is our fervent hope that everything possible will be done by all nations to help, if requested."

News of the accident is scarce. The Soviet government sk,2 sw,-2 ld,10 said yesterday that only two were killed and 197 injured, but U.S. officials claim the casualties are much higher. Europeans have criticized the Soviets for not notifying them about the accident.

"It is an accident, sure, but it seems to me to a certain extent it was blown out of proportion," said Victor Isakov, the Soviet minister-counselor, who is sharing the number two slot at the embassy with another official until a new ambassador is appointed to replace the departed Anatoliy Dobrynin.

"I just read an announcement not only from the government of the Soviet Union but even the government of the Ukraine," he said. "They were speaking of the good quality of the drinking water in Kiev and that the level of radioactivity is decreasing. While we are worried -- it is an accident of a rather unpleasant nature -- everything is being done to stabilize the situation. They said about 196 people were hospitalized and a quarter of them were immediately released."

Sen. John Warner (R-Va.) said the Senate had been briefed on the accident throughout the day but that "most of the information being given to the Senate is in the public domain. I will tell you one thing. Mr. Gorbachev's [Soviet leader Mikhail Gorbachev] credibility has been lowered by his failure to report and the credibility of the U.S. intelligence community has indeed been heightened because of the accuracy of its reports."

Usually the talk at such an event tends toward claims of international friendship rather than international concerns over nuclear energy. At the celebration for the "Impressionist to Early Modern Paintings From the U.S.S.R." last night, there was plenty of the former as well as the latter, despite recent strains in U.S.-Soviet relations over the U.S. raid on Libya.

Along with guests Chief Justice Warren Burger, Walter Mondale and the ambassadors of Hungary, Ecuador and France were the heads of the Pushkin and Hermitage museums, which lent the show's 41 paintings.

"For the exhibit, we decided to choose the best examples," said Hermitage director Boris Piotrovsky, speaking through a translator. "By doing so we are afraid we may have offended our visitors to the Hermitage." He smiled. No translator necessary.

"Painting plays a very important political role today," he continued. "You see these treasures travel around the world, and you feel it is easier to live. People who love art or like music, somehow they are kinder than those who do not like the fine arts."

A sizable contingent of Occidental Petroleum employes also attended. Hammer not only contributed $1.25 million to finance the show's tour, he was instrumental in getting it to the United States at all. He said he had lent a Leonardo da Vinci manuscript to the Soviets, "so they owed me a great favor." When the cultural agreement was signed, he added, "I cashed in my chips."

The show is a dazzle of color, starting with Matisse's "Harmony in Red" and continuing through a series of intimate rooms filled with gardens and portraits.

"Some of them look really very well because these are small rooms," said Ksenia Egorova, curator of paintings at the Pushkin. "Our rooms are much larger."

As part of the cultural exchange, a show of American 19th century art will soon visit the Soviet Union, and this fall Russian paintings from the 19th century will arrive at the Smithsonian. Egorova said that if she could choose something from the National Gallery's collection to bring to Russia, it would be Picasso's "Family of Saltimbanques."

"First, it is a very important and very beautiful painting, and second, we have a study of the female in the show. It has been hung so it is the last painting people see in the exhibit. It's very good. You see the differences. I think it is twice interesting as a combination.