One of the leading post-war American experts on the Soviet Union, the late Charles E. Bohlen, once said that the Kremlin was not a mystery but just a secret. The past few weeks here have again brought into focus Moscow's obsession with secrecy surrounding the health of President Konstantin Chernenko.

The 73-year-old Soviet leader last appeared in public on Dec. 27 at a Kremlin ceremony. His subsequent absence combined with the cancellation of a summit meeting of Warsaw Pact leaders in mid-January has produced a series of rumors about his physical and political health.

All that can be said about Chernenko's absence with a reasonable degree of certainty is that he was hospitalized in early January with an unknown ailment, that his condition was serious at one point, and that he is reported to have recovered to a point that he is convalescing just outside Moscow. He has been described as having a respiratory ailment.

This prolonged period out of the public view has sent Kremlin-watchers scrambling to figure out the next time Chernenko could be expected to appear in public. That appears to be Feb. 22, when the president's schedule calls for him to address the voters in the current election campaign for the Supreme Soviet of the Russian federation.

Since the cancellation of the scheduled Warsaw Pact summit, however, diplomatic and journalistic circles in Moscow have been in a flutter of rumors and speculation. In the context of the secrecy that shrouds the Kremlin, the cancellation took on deeper significance for most observers.

At the same time, as in most countries, the disappearance of a national leader from public view has caused concern and uneasiness among the people. The absence of information about Chernenko has inevitably led to all sorts of largely uninformed speculation.

For those whose job is to inform their readers or governments about the status of leadership in the Kremlin, this is a condition of acute distress.

Virtually all journalists and diplomats rushed to their radios and TV sets today when an American television network reported that classical music was beingbroadcast, often a sign that a major Kremlin figure has died. The report, however, was based on a misunderstanding.

Among other alarming news was a report published in the French newspaper, Nouvel Observateur today quoting U.S. Ambassador Arthur Hartman as saying that he has been told confidentially by Soviet officials that Chernenko had suffered a stroke and was no longer capable of talking.

A U.S. Embassy spokesman categorically denied this report saying Hartman has never said "any such thing."

The exact nature of Chernenko's ailment is not possible to determine, but a clear indication that Soviet officials are seeking to project a posture that their leader is expected to recover and return to his duties came yesterday when a senior Foreign Ministry official told Cable News Network that Chernenko now is "on winter holiday."

The official also denied the reports that the Soviet leader is seriously ill.

Assuming that the official expectation that Chernenko would soon resume his official duties proves correct, there were nevertheless several indications of continuing official concern over his condition, according to western analysts here.

Diplomatic sources reported today that Mikhail Gorbachev, the second ranking figure in the party hierarchy, had cancelled his planned visit to France next week. Gorbachev was to have attended a congress of the French Communist Party and was also expected to meet with President Mitterrand.

It was also announced in the Hague today that the planned visit of Foreign Minister Andrei Gromyko to the Netherlands had been postponed at Gromyko's request. He was to have visited the Netherlands at the end of February or begining of March.

The planned visit of former West German chancellor Willy Brandt in mid-February had been postponed earlier.

Diplomatic sources also reported that Greek officials had been told that it was not likely that Prime Minister Andreas Papandreou, who is to visit Moscow in the first half of this month, would meet with Chernenko. The possibility of such a meeting was not ruled out entirely, however.

All this suggests that something may be amiss. Exactly what, only a handful of men at the top of the Kremlin hierarchy knows for sure. The record demonstrates that they are not given to gossip.

Chernenko has been in less than robust health for 18 months, although he kept a very busy official schedule through December.