Hong Kong — As Alexander M. Haig Jr. prepares to make his first trip to China as secretary of state, key American allies in Southeast Asia have expressed concern over the possibility of a deterioration in Sino-American relations over Taiwan.
Those differences are expected to surface during Mr. Haig's three days of talks with Chinese leaders. China has repeatedly criticized President Reagan's stand on Taiwan, saying any US gestures toward the Nationalist-held island, even under the Taiwan Relations Act, are unacceptable.
Peking has also warned of dire consequences should the United States decide to sell additional military equipment to Taiwan, as currently anticipated. The recent downgrading of Sino-Dutch relations after the Netherlands sold two submarines to Taiwan is a clear indication of what might happen if the administration makes such a decision.
The prospect of a cooling between the US and China has disturbed US allies in the Association of Southeast Asian Nations (ASEAN), especially Thailand and the Philippines. Officials, diplomats, scholars, and journalists from both countries express concern that such a development would hurt US credibility, create more regional instability, and harm the emerging US-China-ASEAN alliance against a perceived threat of Soviet and Vietnamese expansionism.
"It would be disturbing to witness a deterioration in US- China relations as a result of differences over Taiwan," said Philippines Foreign Minister Carlos Romulo. "The Chinese have taken a position that could allow a settlement of the Taiwan question to evolve in the long term.
"There is furthermore the question of American credibility, if the observance of valid commitments [from the US to China] were to be put in doubt."
Mr. Romulo's concern was echoed by Thailand's former Prime Minister Kukrit Pramoj, now an opposition leader in parliament. Commenting on possible US arms sales to Taiwan, he said, "I would be very sorry to see that kind of support and a return to the old balance of relationships between Taiwan, the US, and China. . . . We are now very friendly with China and want to be friends with the US, too."
Suthichai Yoon, editor of Bangkok's respected Nation Review, added, "I think Thailand would rather see a closer -- more cordial -- relationship between Washington and Peking. . . . But Thailand is now not too clear about Chinese- American relations, because after Reagan took over Taiwan has become a sort of new thorn in the whole relationship."
Diplomats in Bangkok said that for Thailand, a strong US- China link is crucial to pressure Vietnam into withdrawing its 200,000 troops from Cambodia. As Thai Foreign Minister Siddhi Savetsila put it, "China can play a constructive role to uphold peace and stability in our area, which we welcome. So we also welcome the US to work closely with China."
Anxiety that the Taiwan issue might threaten such cooperation prompted Mr. Siddhi to raise the matter with State Department officials when he was in Washington in late April. He was told, "The relationship between the US and Taiwan will have nothing to do with the progress of the relationship between the US and the People's Republic of China."
Despite these reassuring words, which are the standard American response to questions on the issue, doubts remain in Bangkok, Manila, and other ASEAN capitals.
On the other side of the fence, Vietnam has also shown interest in the fact that the Reagan administration's more sympathetic view of Taiwan may complicate US-China ties.
The official Vietnamese news media have made no direct comment on the matter. But Hanoi recently announced it had recovered and would soon turn over to US diplomats the remains of three American soldiers listed as missing in action.
Analysts here believe the move was deliberately timed to come just before Secretary of State Haig's Asian tour. Hanoi's goal, apparently, is to demonstrate its continuing good will toward the US, despite American hostility, and signal its interest, in the event of an American estrangement from Chin a, in better relations with Washington.