Stalemated in its relations with the United States, China has apparently begun in the most tentative way to seek some improvement in its ties with the Soviet Union.

In the last few weeks Peking has ended an 18-month delay in sending a new ambassador to Moscow and has worked out new river navigation rules at a meeting with the Soviets, apparently at Chinese initiative.

Both of these steps occurred after the return to power of Vice Premier Teng Hsiao-ping, the Chinese leader probably responsible for sending Moscow an important conciliatory message two years ago.

Some Western experts argue that such a reconciliation could help prod Washington into formally recognizing Peking in order to head off a renewed Sino-Soviet alliance.

"They see some of us saying 'There's no chance of a Sino-Soviet rapprochement so why rush on normalization?" said one Washington analyst. "The Chinese seem now to be saying, 'Well not quite.'"

Recent travelers to China who are familiar with Sino-Soviet affairs say they detect a renewed willingness to deal with Moscow on technical matters.

Analysts here and in Washington who have noted these developments caution against overemphasizing their significance, however. Except perhaps for a brief period when the Amur and Ussuri rivers agreement was being negotiated, the Chinese have not slackened their propaganda war against the Soviets. Just in the past week, the official Chinese press has referred to the Soviet Union as a "bully," making a "bid for world domination" and as "the most dangerous source of war at present."

There has been no sign that the two nations have resolved their fundamental dispute over who owns vast tracts of land along their common border. Teng was quoted by West German visitors last month as saying that a "warming up" of Sino-Soviet relations was "out of the question even for the next generation."

Yet, it has been canon of Chinese foreign policy that state-to-state relations might proceed even between bitter ideological foes - a principle seemingly forgotten in the last few years when the most rabidly anti-Soviet Maoists were influential in Peking.

Since Mao's death and the purge of his most racial disciples, Western experts have argued that it would make sense for Peking's new, more pragmatic leaders to try to ease Sino-Soviet tensions. In addition to prodding Washington, this would allow Peking to make better use of men and materials now engaged in guarding the Soviet border.

The last important Chinese gesture to the Soviets occurred on Dec. 17, 1975, when Peking suddenly announced it was releasing three Soviet helicopter crewmen it had captured 21 months before. The Chinese admission that the Soviets had been judged "credile" in their claim that the helicopter had accidentally strayed into Chinese territory represented a stunning turnabout. Previously, the Chinese had charged that the Soviet claim was "bunch of lies" and that the crewmen were spies.

At the time of that turnabout, with both Mao and Premier Chou En-lai ailing, Ten was effective command of the day-by-day operation of the Chinese government. Chou, Teng's political patron, died 12 days later and Teng was quickly purged by Politburo members close to Mao who launched a thinly disguised press attack against his alleged attempt to "betray the nation" to the Soviets.

In the few months after the death of Mao and the purge of his dogmatic disciples last fall, there was no hint of a change in the Chinese attitude toward Moscow, despite several Soviet gestures toward the new administration of Chairman Hua Kuo-Feng.

The few new developments have come since Teng's official reinstatement in mid-July as the party's No. 3 leader.

One recent traveler to Peking who has known the Chinese for several years said he detected a new attitude indicating that despite irreconcilable differences with the Soviet Union, "it's there and so why not deal with it?"

Hua, in his lengthy political report to the 11th national party congress Aug. 12, said. "The Soviet leading clique has betrayed Marxism-Leninism." But he added: "At the same time, we have always held that China and the Soviet Union should maintain normal state relations on the basis of the five principles of peaceful coexistence." So far, Hua said, the Soviets had "not shown one iota of good faith about improving state relations . . ."

When Wang Yu-ping, the new Chinese ambassador to Moscow, arrived at his post two weeks later, he was greeted by an anti-Chinese broadside in the Soviet ress. The Chinese said health problems had helped cause the 18-month delay in replacing Wang's predecessor. It was not clear if Wang's arrival meant anything significant.

On Oct. 4, however, the official New China News Agency gave somewhat lengthy coverage to a Soviet massage celebrating China's national day. On Oct. 6, the Chinese announced they had reached "agreement on a number of issues" concerning navigation of rivers along the Sino-Soviet border. On Oct. 10, Soviet Premier Alexel Kosygin received Ambassador Wang, a courtesy that some analysts here found more significant than the Chinese decision to send Wang to Moscow in the first place.

The river navigation agreement came after eight years of fruitless talks, which had been suspended in 1974. The new pact remains a purely technical agreement with no immediate impact on the vastly more important issue of where the Sino-Soviet border line should be drawn.Nevertheless, it apparently provides rules for navigation of the heavily-trafficked junction of the Ussuri and Amur rivers and thus reduces chances of boat collisions that could turn into serious border incidents.

"The Chinese had to do something. The situation was endangering lives," said one European diplomat here. "But it's odd they would do it now when the place is all frozen up there." Most analysts say that the centuries-old fears the Chinese and Russians have of each other will prevent any return to their friendship of the 1950s. Hua and Teng are also expected to softpedal any agreements they make with Moscow for fear of drawing domestic political criticism that they have forgotten such Soviet "crimes" as the withdrawal of all technical assistance from China 17 years ago.