Four thousand people, among them His Imperial Highness Prince Takamatsu, younger brother of Emperor Hirohito, gathered today on the top floor of the Takashimaya department store for the opening of the Phillips Collection in Japan.

Yomiuri Shimbun, a Japanese newspaper, has paid the Phillips $200,000 for "Impressionism and the Modern Vision: Master Paintings from the Phillips Collection." The newspaper, which has a daily circulation of 13.6 million, also has agreed to pick up all the bills for the traveling exhibit.

"It will help us a lot," said director Laughlin Phillips, whose private gallery is now being renovated. The Japanese exhibition is essentially the same show that has already toured five American cities since July 1981.

While the Phillips Collection's galleries are closed, 40 of its paintings are on temporary view at Garfinckel's, the Washington department store. Ninety other paintings, including some of the most famous, have been carefully installed in the 3,000-square-foot galleries on the Takashimaya store's eighth floor.

The Japanese admire the art of the Impressionists because it is easy to understand, according to Katsuya Nakamura, the store's public relations officer. "Earlier art is more religious, later art is too abstract," he said.

Denys Sutton, a British art historian, picked the Japanese exhibit. He chose Renoir's "Luncheon of the Boating Party" (1881), Georgia O'Keeffe's "From the White Place" (1940), as well as canvases by Monet, Matisse, van Gogh, Rothko, Dove and Guston.

"I'm an example of the Japanese who like Impressionism," said schoolteacher Shigefumi Ito, 47. "They are my favorites because they are bright and clear."

"It's the first time I've ever seen such a comprehensive collection," said college freshman Seiko Sadano, 18. "I can enjoy making comparisons."

It is not only the Phillips' first showing in Japan but also its first major exhibition overseas. "We have lent individual paintings abroad before," said Laughlin Phillips, "but this is the first time we've ever sent our best things abroad as a unit. They're beautifully installed, the lighting is excellent and the interaction between the private sector of newspaper, department store, museum and the public is exciting."

Most of Japan's department stores include top-floor art galleries. The assembling of important shows is a boon to both the store's business and its prestige. Admission to the Phillips show is about $3.75 for adults and $2.50 for students. The catalogue sells for about $7.

The mood at the opening was one of good feeling and high adventure.

"It's splendid. It's wonderful. It's so comprehensive that everyone can find something they like from the easy Renoir to the more difficult Klee," said a 61-year-old businessman. "I can't tell you my name. I escaped from the company for this afternoon."

William Clark, deputy chief of mission at the American Embassy, said: "It's just like visiting old friends."

"I'm very impressed," said Erich Steingraber, general director of the Bavarian State Galleries in Munich. "I saw it about 20 years ago in Washington when I was working in the Metropolitan. It's fantastic. So many masterpieces. This is a big event for Japan."

"Seeing the real 'Boating Party,' engraving it on my heart, is most important to me," said Ichiro Yoshikuni, former director general of the government's Cabinet Legislation Bureau.

An article in the weekly magazine of the Yomiuri Shimbun newspaper urges readers to see "at one glance all of western art history."

If Kazunari Ogawa, Yomiuri's chief of cultural promotions, is right, thousands of Japanese will do just that. He expects 6,000 daily viewers and perhaps as many as 10,000 during the last days of the show.

"The Phillips Collection of Washington, D.C., U.S.A.," as the posters label it, will remain at Takashimaya until Oct. 4. From Oct. 29 to Nov. 13, it will be on display at the Nara Prefectural Museum in the eighth-century capital of Nara in western Japan.