Mitsui & Co., the American subsidiary of Japan's oldest trading company, has joined hundreds of other national and international firms in opening a government relations and public affairs office here.

Mitsui executive A. E. Klauser denied that the company's move is in response to anti-Japanese sentiment among some Americans because of increased Japanese imports into U.S. markets.

"Chairman (Yoshizo) Ikeda has indicated for the last several years that he beleives Mitsui should become internationalized," said Klauser, the company's senior vice president and director of the Washington office. "When you become internationalized, you have to be able to understand the pulse of the nerve centers of every country you're going to operate in.

"Washington is that pulse. It has become the pulse center of the nation. This has been understood and foreseen by Mitsui.

"Our function and purpose is not to sell to the government," Klauser said, "but to learn more about what's going on in Congress and the administration and establish a dialogue with Congress, the agencies and so on."

Without that communication, a company can "end up with an adversarial, competitive relationship," Klauser added.

The company boasts of its export promotion program, which it said has resulted in more than $1.3 billion in new American exports to Japan in the past two years and denies there is significant anti-Japanese sentiment to hurt its business.

"I don't think there is a general feeling like there was in 1978 when people were up in arms over Japanese imports," Klauser said. "The American people and the American Congress have learned more about their own productivity. . . and no longer are they loathe to blame some other country."

Despite Klauser's optimism, many presidential candidates have used the Japanese trade issue to agitate campaign crowds. United Auto Workers President Douglas Fraser and others in the auto industry have blamed Japanese import cars for low U.S. sales and profits.

In addition, U.S. Steel, the nation's largest steel producer, is preparing complaints against Japanese steel makers, charging them with dumping steel products on U.S. markets.