Dramatic changes in Asian policy loomed large on the agenda of the Reagan administration when it came to office. But since then the Chinese communists have reasserted their fabled diplomacy, and Japan has reasserted its fabled stubbornness. The current Asian visit of Secretary of State Alexander Haig announces that the possibilities for useful changes across the Pacific are small.

A hardening of Asian pressures on Soviet power was strongly advocated by the new adminsitration. The president and his chief advisers talked both of rearming mainland China and sending more sophisticated weapons to Taiwan. They called on Japan to play a larger role in Pacific security. There was at least some thought of prying Vietnam from the Soviet embrace.

In China, however, those hopes ran athwart an unresolved internal struggle. The top leader, Deng Xiaoping, has pushed a program of economic modernization at the expense of the military. The People's Liberation Army has suffered a loss of prestige, cuts in manpower and a demotion to last place in the bidding for technical resources. Some Chinese generals have apparently teamed up with the political opposition to Deng. Among other complaints against him, they have evidently laid the charge that his normalization of ties with the United States in 1979 did not preclude greater American support for Taiwan. Since Deng, unlike Mao Tse-tung, has to prove his legitimacy, the soft-on Taiwan charge carries resonance.

Deng exploited this vulnerability with characteristic boldness. He turned aside a proposal from the Reagan adminsitration for a visit to Washington by the Chinese foreign minister, who carries no political weight in Peking. Instead he pressed for, and got, a visit to Peking, where the whole Chinese leadership can be present. He turned aside a suggestion that the visit come from the vice president and former ambassador George Bush, whom the Chinese distrust. Instead he pressed for, and got, a visit by Secretary Haig, whom the Chinese regard as a friend. He turned aside a suggestion that the meeting take place in the fall. Instead he pressed for, and got, meeting before a hardening of relations between Taiwan and the Reagan administration.

In the days preceding the Haig visit, the Peking press was full of hostile references to Taiwan. It was repeatedly asserted that the People's Republic would refuse military aid from the United States, if the price was an increase in American arms shipments to Taiwan. So in promoting Sino-American strategic cooperation against Russia in Peking. Haig has been pushing back -- perhaps to the never-never time -- the sending of sophisticated American weapons to Taiwan.

In Japan, the Reagan administration ran into the growing difficulty the political leadership and the bureaucracy face in trying to elicit sacrifice from a society pushing relentlessly for material prosperity. After much wrangling, Prime Minister Zenko Suzuki did undertake, on a state visit to Washington, to increase Japanese defense efforts.

But there followed a tremendous fuss in the Diet about the use of the word "alliance" in the communique summarizing the Reagan-Suzuki talks. Suzuki was obliged to change foreign ministers. The Japanese stop on Haig's Asian trip was cancelled. It is now evident that it will be a long, long time before Japan plays a significant role in pacific security.

The significant role the Japanese do play in Asia is economic. In return for access to raw materials, the Japanese have become major suppliers of capital and aid to all the countries around the Pacific basin, including those (Indonesia, Malaysia, Thailand, the Philippines and Singapore) grouped in the Association of Southeast Asian Nations. Haig will bless that arrangement by attending an ASEAN meeting in Manila this week.

But the ASEAN connection mortgages policy toward Vietnam. Two of the ASEAN countries -- Thailand and Singapore -- strongly oppose Vietnam's drive to gobble up Cambodia. They are outdone in that tough stance by China -- the only true backer of the Cambodian regime. Japan tends to follow China on that question. So by latching onto China, Japan and ASEAN, the Reagan administration forgoes the chance to pry Vietnam from the Soviet Union.

Continuity far more than change, accordingly, characterizes the American role in Asia. That is no bad thing for the foreign policy of a great power, particularly in an area where developments have been generally favorable. The good thing that has yet to come is an explicit recognition by the Reagan administration that it does not have to do everything differently -- that previous policies are not all bad.