Peking — Sino-American relations seem to be emerging from the sourness that has characterized much of the past year. The textile agreement reached in Geneva July 30 after arduous negotiations is one sign of the improved atmosphere. Defense Secretary Caspar Weinberger's planned visit to Peking Sept. 25 to 29 is another sign, as is Chinese Foreign Minister Wu Xueqian's plan to visit Washington in October.
The clearest indication of better relations would of course be a visit to Washington by Chinese Premier Zhao Ziyang. Mr. Zhao has already accepted President Reagan's invitation in principle, but no date has yet been fixed. A visit by Mr. Zhao this year could open up the possibility of a Reagan visit to China before the presidential election campaign goes into full swing next summer.
Taiwan is still the chief sticking point in Sino-American relations. Senior leader Deng Xiaoping said recently that ''people in power in the United States have never given up 'two Chinas' or 'one China and a half.' ''
He also twitted President Reagan, without referring to him by name: ''A (US) president says one thing during the campaign, another when he takes office, another during the mid-term election, and still another near the next general election.''
Despite this built-in obstacle to better relations, Peking and Washington have recently made progress on a number of substantive issues. For instance, the possibility of American participation in Peking's ambitious nuclear energy program has opened up following talks in Washington between Chinese and American officials.
Hitherto the US has been demanding that Peking open its nuclear facilities to international inspection and that it sign the nuclear Non-Proliferation Treaty. Otherwise, the US said, it could not allow American firms to supply reactors to China for civil use.
But Peking refused, and eventually Washington agreed to withdraw its demands.
Peking is also considering joining the International Atomic Energy Agency, based in Vienna. Hans Blix, director-general of the IAEA, is visiting China in mid-August. If Peking joins, then the US would consider it ''a positive step,'' an American official said.
So far, Framatome of France is considered to be the candidate with the best chance of landing a large reactor order from China. But Framatome's reactor is in fact made under license from Westinghouse. Washngton's new flexibilty may once again focus Peking's attention on the possibility of buying reactors directly from American suppliers.
Peking has lately also shown signs of movement over the deadlocked Huguang railway bonds issue. Till now Peking had refused to appear in court to defend itself from nine American claimants who charged China with defaulting on railway bonds issued in 1911 by the then imperial Qing government.
Now it is understood Peking has agreed to the State Department's longstanding suggestion that it hire an American lawyer to put forward its argument that, as a sovereign government, it should be immune from prosecution in another country's courts.
Finally, on the question of transfer of dual-use high technology to China - technology that can be used for either civilian or military purposes - US government agencies are now understood to be working on specific guidelines that it is hoped will be ready before Mr. Weinberger's visit to Peking.
In May Commerce Secretary Malcolm Baldrige took to Peking the announcement that President Reagan had decided to put China in the same category as friendly or allied nations, but with specific guidelines that would still restrict the sale of certain technology. Peking is awaiting the result of the guidelines exercise to see what will be made available to it and what it would like to buy.
The textile talks were prolonged and difficult. Washington was caught between American textile manufacturers arguing for greater restrictions on Chinese textiles and American farmers suffering from China's embargo on purchase of important categories of agricultural crops. Details have not been disclosed but China will get a slight increase in its exports to the American market.