Japan's incoming ambassador to the United States promised today to work to open Japanese markets further to U.S. products and said his government's past efforts to do so "have not been sufficient."

"We owe to the United States our present prosperity," Nobuo Matsunaga said in an interview. "I believe it is our own responsibility to open up more [of] our domestic market to foreign products."

Matsunaga will arrive in Washington late this month, as negotiations over sales of U.S. telecommunications products in Japan -- one of the thorniest trade disputes between the two countries in recent years -- come to a head.

Offering generally conciliatory words during a time of heightened trade tension, Matsunaga stressed Japan's long friendship with the United States and ways his country had benefited from the postwar economic and military order the United States created.

He offered no specifics on how liberalization would be accomplished, beyond noting that his government is working on a variety of market-opening measures that will be made public soon.

Matsunaga, 62, a career diplomat who will be serving his first tour in the United States, said Japan has no desire to continue the trade imbalance that resulted in the United States' $34 billion trade deficit with Japan last year.

He played down common explanations here that blame the deficit largely on the United States: the strong dollar, U.S. budget deficits and U.S. firms' alleged lackluster product quality and marketing skills. These play a role, but do not excuse Japan for failing to make efforts on its own, he said.

In the past, Japan was accorded special advantages, akin to a golf handicap of 36, Matsunaga said. "Now we have become a little bit stronger player. If we continue to insist on a 36 handicap in competing, say, with the United States, that would not be fair," he said.

Matsunaga replaces Yoshio Okawara, an urbane and personable careerist who has traveled widely in the United States since his appointment in 1980 and who has won high marks for a type of down-home diplomacy and skill in resolving conflicts between the two governments.

Matsunaga brings to the job more of the self-effacing style of the Japanese civil service. His English is less fluent than Okawara's, and his demeanor is less open. But he is generally regarded as a highly competent diplomat who made his way to the top of an extremely competitive ministry.

Both men are products of the elite track of Japan's mammoth governmental bureaucracy, which wields higher sway in decision-making than the federal bureaucracy in the United States.

Political ambassadors are highly unusual in the Japanese system. However, Matsunaga is known for being a bit closer to politicians and business leaders than is the norm for ambassadors.

Matsunaga said he enjoys "the confidence" of both Prime Minister Yasuhiro Nakasone and Foreign Minister Shintaro Abe. Matsunaga said that in a meeting with Nakasone yesterday, he told the prime minister that his first task in the United States would be to get to know "how the United States, or Americans, are looking at Japan."

Born in Tokyo in 1923, Matsunaga attended the elite Tokyo University, graduating from its faculty of law in 1944. He has served abroad in the Soviet Union, France, Switzerland and, most recently, as ambassador to Mexico. Since 1983, he has held the position of vice minister for foreign affairs, the Foreign Ministry's highest career job.

Like many Japanese heading for a U.S. assignment, he looks forward to improving his golf game -- courses here are exhorbitantly priced. His other main personal interest is European cuisine.

In his closing days in Japan, he is spending much of his time learning about the economic relationship with the United States. Last week, he visited a Nissan Motor Corp. Ltd. auto factory. On Wednesday, he will go to a telecommunications plant run by the electronics giant NEC.

One of his first official tasks after arriving in the United States will be to fly to Fremont, Calif., for inaugural ceremonies involving the newly formed joint-venture car manufacturing company of General Motors Corp. and Toyota Motor Corp.