State Department officials reacted warily yesterday to Sunday's announcement in Peking that China and the Soviet Union have agreed to reopen regular negotiations after three years of deep freeze.

Any change in ties between China and the Soviet Union would mark the first shift in the Peking-Moscow-Washington equation since the United States and China put their relations on a normal footing.

It would also further complicate Reagan administration policy making at a time when disgruntled supporters of Taiwan are carefully watching for who is named assistant secretary of state for East Asian affairs in place of John Holdridge, recently selected as the new U.S. ambassador to Indonesia. Several major decisions on U.S. trade relations, particularly oil exploration and advanced technology exports, are expected in the near future.

"We would be foolish to say we aren't watching it but we don't know yet what directions they are going in," said one State Department official about the preliminary round of Sino-Soviet negotiations just completed in Peking. "As for subtle areas of warmth, it's a little early to say what they will be. I don't see anything changing our policy toward either of them."

U.S. China watchers have rejected suggestions that Peking is about to play a "Soviet card." They say feints toward Moscow could well be part of internal political maneuvering between factions in Peking and point to Chinese statements about the primacy of Peking's ties with Washington.

But this analysis draws attention away from public and private indications from Chinese officials that Peking is clearly expecting a change in its relations with Moscow, even if the process is long and drawn out and stops short of putting Soviet relations on a par with the United States. It also ignores recent signals of Chinese irritation with the U.S. relationship.

Adding to the possibility for change in Sino-Soviet relations are developments in Afghanistan. Asian and American diplomats note that the Soviet Union has been somewhat more forthcoming in recent U.N.-sponsored talks, although Chinese officials indicated no change in Moscow's stance in the Peking talks.

Soviet negotiators reportedly have agreed on an agenda for Afghanistan discussions that include as a package the three critical areas of Soviet troop withdrawal, return of refugees and external guarantees for Afghan security. Western diplomats caution, however, that there are many "purely tactical" reasons why Moscow might display greater flexibility.

The Afghanistan developments could be significant because U.S. officials have emphasized that the Chinese had set as conditions for any change in long-frozen Sino-Soviet relations the removal of troops from the troubled Sino-Soviet border, an end to Soviet support for Vietnam's operations in Cambodia, and a withdrawal of Soviet forces from Afghanistan.

Foreign diplomats familiar with Chinese thinking say Peking's position is not quite so rigid, however. They say progress in one or two of these areas -- such as a commitment by Moscow to reach a peaceful settlement in Afghanistan and to pull out its troops -- might open the way for more far-reaching changes in the Sino-Soviet relationship.

In the short run, these diplomats say U.S. policy makers should be prepared for announcements that the two countries are about to conduct more exchanges in the scientific, cultural and athletic areas. The Chinese are said to argue: "You carry out all kinds of exchanges with the Russians and learn a great deal about Soviet thinking from them. Here we have a long border with them, yet we isolate ourselves and know little about what goes on there."

The talks between Soviet Vice Foreign Minister Leonid Ilichev and Chinese Vice Foreign Minister Qian Qichen that ended in Peking last week were the first formal high-level contacts between the two countries since Peking broke off discussions in 1979 when Soviet troops entered Afghanistan.

At the recent Chinese party congress, top-level officials made it clear that relations with the Soviet Union were about to be put on somewhat more of an equal footing with those of the United States. At the same time, renewed criticism of U.S. policy on Taiwan and trade relations has emerged from ranking Chinese officials.

One prominent signal came in a speech two weeks ago by Foreign Minister Huang Hua before the Council on Foreign Relations in New York. Speeches before the council are by custom off-the-record, but the Chinese news agency Xinhua nevertheless carried a lengthy account of his remarks.

In the Xinhua account, Huang began by outlining "favorable conditions" for U.S.-Chinese relations, but then added: "There is no difficulty from the Chinese side in the further development of Sino-U.S. relations. However, I regret to say that the development of our bilateral relations is not free from obstacles."

Chief among these obstacles, according to the Xinhua account, is continuing U.S. support for Taiwan. There was no mention of the Sino-U.S. communique on Taiwan issued last August.

Huang went on to charge the United States with intensifying discrimination against China in trade relations and in scientific and cultural exchanges, particularly citing restrictions on the export of high technology and sophisticated equipment to China.

" . . . I once said that the U.S. authorities had made many nice remarks about developing our bilateral relations. Yet, what has happened can be described by a Chinese saying, 'loud thunder, little rain.' . . . In view of recent developments, one cannot help but asking: Does the U.S. government regard China as a friend or an adversary?" Huang is quoted as saying.

Xinhua concluded Huang's remarks by quoting him as saying he hopes for a positive approach from "farsighted U.S. statesmen." But just before this remark, he warns: "We neither play the U.S. card nor the Soviet card. At the same time, we will never permit others to take China as a card. The Chinese mean what they say and they are serious in their statements."