WASHINGTON — RELATIONS between the United States and China have slid to perhaps their lowest point since the aftermath of the Tiananmen Square massacre of 1989.
The US, for its part, is openly furious over Beijing's detention of an American human-rights activist, and quietly concerned about evidence that China has sold medium-range missiles to Pakistan. China is still smarting from Taiwanese President Lee Teng-Hui's visit to Cornell University - an ''unofficial'' trip that Beijing believes reflects an overall lack of respect for China's importance on the part of the Clinton administration.
There is little reason to believe this atmosphere will warm up anytime soon. The decline of the Soviet threat has removed a major geostrategic force that pushed the US and China closer together. In addition, China appears to have entered a stage of political turmoil, with nationalist and military forces exercising greater power as its Old Guard civilian leadership ages.
Thus US diplomacy is now in a bad way in Asia. China has become chilly at the very time Japan, the other major regional power, is wrangling with Washington over trade disputes.
A shift in attitudes
''I think Asian attitudes towards the US are in the process of shifting in fundamental ways,'' says Casimir Yost, director of the Georgetown University Institute for the Study of Diplomacy. ''There is a greater discounting of American importance in the region today than there was even a couple of years ago.''
Similarly, US government attitudes towards Asia may be shifting. In its first year or so in office the Clinton administration often went out of its way to emphasize that the world was changing and Asia was rising in importance, compared with the West.
More recently that interest has waned, while the State Department has turned its attention to foreign-policy crises elsewhere, according to Yost. ''I think that traditional US interests in Russia, Europe, and the Middle East have reasserted themselves,'' he says.
A missing American
Still, US diplomats have sounded quite worked up of late over the case of Harry Wu, a Chinese-born US citizen who entered China on June 19 and is now in detention somewhere in the country.
As of this writing, US diplomats had not been allowed to talk with Mr. Wu, and were scouring western China in an attempt to find him.
Wu has visited China often in the past to conduct research on what he claims to be its extensive network of prison labor camps.
While his work may be irritating to the Chinese, Wu had a valid visa, and thus had a reasonable expectation of traveling unhindered, say US officials.
''It is inexcusable that they're holding an American citizen,'' said State Deptartment spokesman Nicholas Burns on Wednesday. ''This is not normal diplomatic practice.''
In unusually frank language, Burns indicated that the ''bizarre'' Wu situation was only one of a number of difficulties between the US and China.
He indicated, however, that the US was trying to communicate with Beijing and work through this difficult period. ''The United States and China have an enormous stake in the future of our relations,'' Mr. Burns said.
Chinese officials on Wednesday told the visiting ex-Secretary of State Henry Kissinger that they were not at fault for the Wu incident.
Chinese Premier Li Peng went so far as to tell Kissinger that China's response to a number of recent problems with the US has been mild - something the US should not take as ''a sign of frailty.''
The May visit of the president of Taiwan, a nation China regards as nothing more than a renegade province, still appears to bother the Chinese. In response to the trip Beijing withdrew its ambassador from Washington and canceled meetings concerning the control of missile and nuclear-energy technology.
It's true that ''we made a muck of things with the visit,'' says Elizabeth Economy, an associate fellow for Chinese studies at the Council on Foreign Relations.
The US raised the profile of what would otherwise have been a quiet trip by first denying Mr. Lee a visit, then allowing him in after concerted Congressional pressure.
''We need to let the Chinese know they are still very important to us,'' says Ms. Economy, through such measures as the scheduling of high-level meetings and reiteration that the US does not support a unilateral declaration of independence on the part of Taiwan.
The wild card in the whole dispute could be China's alleged sale of M-11 missiles to Pakistan. If officially confirmed, such a sale would under US law force American officials to move to cut off trade with China.
Last year the US bought some $30 billion worth of Chinese goods, while selling about $9 billion worth in return.