Moscow — Moscow enters its third round of Sino-Soviet ''normalization'' talks sensitive to recent signs of a thaw in China's ties with the Reagan administration.
Soviet officials are hopeful the talks, reopening today in Peking, will help further last year's striking improvement in atmosphere between the communist giants.
But the officials suggest it will take considerable time to resolve key issues of substance and convert any atmospheric improvement in relations into something deeper.
''In Asia, for instance, our policies are starkly different. Our friends are China's opponents, and vice versa,'' one Soviet official commented to the Monitor on the eve of the renewed talks.
Soviet sources suggest the recent announcement that Mr. Reagan plans to visit Peking next year has reinforced an existing assumption here that Sino-Soviet normalization will inevitably stop far short of the kind of alliance existing before the communist powers' split two decades ago. A revival of party-to-party ties, as opposed to improvement of state-to-state relations, ''is not even at issue yet,'' noted one official here.
''China doesn't want to be under either our wing or the US wing,'' added a prominent Soviet China expert Monday. ''China wants to be 'a new center' in the world political equation.'' This official said he had long felt China's ''increased interest'' in ties with the West and Japan, would survive any rapprochement with Moscow.
First, he said, this interest was dictated by China's bid to modernize its armed forces. Second, the Chinese need huge investment for economic modernization. He spoke of ''obstacles'' in ties with Mr. Reagan, notably ''Taiwan, and the fact Reagan is no more fond of Chinese communism than of Soviet communism.''
''But I think we are witnessing a stage in the general drift of China toward the West . . . I think there may be quite serious agreements in the foreseeable future - on issues like technology, or modernization of the Army - if the Americans are interested.''
The official, and others interviewed, do expect a gradual, parallel improvement in China's ties with Moscow. Both sides, the officials said, want this.
The countries' shared ''socialist systems,'' and China's desire for various forms of economic cooperation with the Soviets, are seen here as potential prods toward a further Sino-Soviet thaw. And both sides, Soviet sources point out, benefit by reduced border tension.
Soviet officials say the ripest area for substantive improvement of ties is the countries' once tense border. Military ''confidence measures,'' or troop cuts, are cited as possibilities for discussion.
And while China says it will introduce, in the current round of talks, a move to get the Soviets to reduce their force of modern SS-20 missiles near the frontier, officials here indicate Moscow has no objection to nuclear arms talks with Peking.
The open question is whether Peking seeks such talks in isolation of what Moscow terms ''obstacles'' raised by China on ''third-country'' issues. China wants Soviet concessions on Afghanistan, and on allied Vietnam's troop presence in Kampuchea.
The hunch among Soviet sources, who add that even an accord on border issues would likely be a slow process, is that China is not so inclined at present.
Of atmospheric improvement, however, there can be no doubt: academic, cultural and scientific exchanges - in the deep freeze during 20 years of Sino-Soviet estrangement - are being revived. Trade between the two countries, though still nowhere near pre-split levels nor near the level of current Chinese commerce with the West and Japan - is also undergoing a renaissance.