American Security bank of Washington has become the first area financial institution to open an office in Japan.

Already engaged in extensive banking relationships with China, as one of the first five U.S. institutions with a Bank of China correspondent relationship in the early 1970s, American Security will concentrate on Asian international markets from its new office in Tokyo.

The office will be headed by Sensaburo Sunemastu, previously a Citibank official in Tokyo and San Francisco for 35 years. He joined the Washington bank last summer, and Japan's government recently approved American Security's application to open its liaison office in Tokyo.

Other than banking facilities in the Caribbean, the only other international representative office by a local bank is a Riggs National Bank office in London.

Although the Tokyo facility will not take deposits or operate as a commercial bank branch, its operations will be similar to domestic loan production offices of American Security now open in Richmond and New Orleans.

Tsunematsu, who was in Washington recently before returning to Tokyo, described the office as "eyes and ears" for American Security in Japan. Among his duties, he said, are "to let the Japanese know about ASB as a commercial bank with international operations."

American Security is the Chinese government's main banking institution in the U.S. and ASB Chairman Carleton Stewart is planning a trip to Peking next May, his second in two years, in the wake of growing interest by Peking leaders in establishing business and economic ties with this country.