The Kremlin's chief spokesman denounced the Reagan administration today as "the most militaristic and reactionary" American government since World War II.

This harsh assessment was distributed by the official Soviet news agency Tass only hours before Soviet Foreign Minister Andrei Gromyko and Secretary of State George P. Shultz were to meet in New York, and as a new round of arms talks was to start in Geneva this week.

The Kremlin spokesman, Leonid Zamyatin, charged in his article that the Reagan administration is "sabotaging disarmament talks," and dismissed White House claims that it is seeking to reduce strategic and intermediate-range nuclear arms as "nothing but hypocritical rhetoric."

The Kremlin's message seemed loud and clear: Current U.S. policy precludes the possibility of a meaningful dialogue.

The Kremlin's top expert on U.S. affairs, Georgy Arbatov, Tuesday sounded a similar note in an interview with Reuter. He described the Reagan administration as "absolutely hostile," but stressed that Moscow has time to wait for American policy to change. Arbatov, a key aide among a small group of officials who advise the ruling Politburo, contended that he is "absolutely sure we will keep the door open" for talks.

Such comments have set off a guessing game here about whether the Kremlin has given up hope on getting anywhere with Reagan. Stated somewhat differently, the question is whether Moscow intends to risk a slide toward confrontation or whether it could be pushed at Geneva to come closer to negotiating on Reagan's terms.

Generally, Western diplomats here believe that the Russians still want to talk to Washington. Soviet rhetoric, they say, frequently differs from Soviet behavior at the negotiating table. The Soviet proposal to cut Moscow's strategic force by 25 percent for a somewhat smaller cut in the U.S. force (plus a ban or limit on cruise missiles and the D5 missile for Trident submarines) was seen as an encouraging step.

However, in this view the Russians are not to be expected to yield beyond certain limits on arms control issues, which comprise the core of Soviet-American relations. Nobody knows what these limits are. But some specialists suggested that they could be discovered in the two sets of Geneva talks on strategic and intermediate arms.

So far, Moscow has been coping with Reagan's hard position by working actively to improve relations with Western Europe and by openly courting China in an effort to reduce tensions on its eastern borders.

There is a glimmer of hope here that Peking has decided to respond positively to repeated overtures for the resumption of Sino-Soviet political contacts, although it is apparent that the extent of these contacts due to start next month would be determined by the Chinese.

However, the possible collapse of West German Chancellor Helmut Schmidt's government has opened gloomy prospects for Moscow's policy toward Western Europe.

Schmidt's Social Democratic Party contains a powerful left wing which has opposed the scheduled deployment of 572 new American medium-range nuclear missiles in Western Europe in 1983. And Schmidt has assumed the role of "interpreter" between the two supowerpowers in an effort to influence the talks on curbing "Euromissiles."

Diplomats here say it is not likely that a new Bonn government would abandon detente entirely. Commercial relations, for one, are not likely to be affected. But if the Social Democratic-dominated Bonn government should fall, that would clearly be another setback for Moscow.

The Russians are carefully following developments in Bonn. It is possible, according to some analysts here, that the eventual outcome may be a somewhat more accommodating Soviet stance in Geneva. It is equally possible that, confronted with a hostile U.S. administration and continued difficulties throughout their empire, the Russians may go in precisely the opposite direction.

Public voices here suggest a tough attitude. Marshal Viktor Kulikov, the commander of Warsaw Pact forces, spoke last week of the international situation as being the most dangerous since World War II. Defense Minister Marshal Dmitri Ustinov has blamed Washington for policies which "tend to destabilize" the situation.