Central Intelligence Director William Casey, in an unprecedented surprise visit to Japan, today asked Prime Minister Zenko Suzuki to increase the country's economic assistance to Asian countries.

According to Japanese officials, Casey espically asked for an increase in aid to Pakistan and Thailand, countries that lie on the fringes of areas of communist expansion in the past two years.

Casey's visit to Tokyo was not announced in advance and his presence was not known until his name appeared on a list of visitors to Suzuki's office this morning. So far as Japanese officials could recall, it was the first official-level discussion between an American CIA director and an incumbent Japanese prime minister.

American officials declined to elaborate on Casey's mission. They described his visit with Suzuki as a "courtesy call" and said he had come to Tokayo primarily for talks with Ambassador Mike Mansfield.

A brief embassy statement said Casey and Mansfield informally discussed "general international developments in East Aisa" and that Casey had sought the ambasssador's views on "political, military and strategic trends in the Pacific region.

U.S. officials said there were no substantive discussions between Casey and the prime minister. But Japanese officials told reporters that Casey had talked about China and the general Asian situation in addition to raising the issue of aditional economic assistance.

THE U.S. has pressed Japan repeatedly to play a bigger global role commensurate with its economic power. Washington has ased for a larger Japanese military commitment to joint defense in Asis and has urged Japan to continue to enlarge its economic aid programs.

Japan has made it clear it will not increase insubstantialy its defense budget this year but has promised another surge in aid that will double its economic assistance programs by 1985.

Japan, at the request of the United States, granted an extra aid package to Pakistan after the Soviet invasion of Afghanistan, largely to help the Pakistani government cope with refugee problems.

Thailand has benefited from Japanese aid for Cambodian refugees who swarmed into the country after the Soviet-backed Vietnamese invasion of Cambodia. On a recent trip through Southeast Asia, Suzuki announced a new aid package for internal Thai development.

According to Japanese officials, Casey brought up the subject of aid to b oth countries. He reportedly said that the United States appreciated past Japanese commitments to them and asked that more be done in the future.

Casey also said that the future of Cambodia should be discussed when Japanese Foreign Minister Masayoshi Ito comes to Washington later this month.

Casey was not available to reporters here. He arrived Saturday night and held discussions with Mansfield Sunday and today, U.S. officials said.

They discussed China, Southeast Asis and the Persian Gulf region, officials said, but no details of their talks were made public.