Admittedly, it has become a cliche to quote Winston Churchill's description of the Soviet Union as ''a riddle wrapped in a mystery inside an enigma.'' But the simple fact is that Yuri Andropov is rapidly becoming the personification of that phrase.
In truth, not much is known about the man who holds the most powerful position in a country that covers one-sixth of the world's land surface.
The lack of information about Yuri Andropov is a bit unsettling for Western countries accustomed to highly visible leaders. And it presents Western leaders with perhaps their greatest challenge in dealing with the Soviet Union. They simply don't know much about the man who is in charge - or, indeed, if he is in charge.
Yuri Andropov dropped from public view on Aug. 18, 1983. He canceled trips and meetings with foreign leaders and failed to show up at important state and party functions.
In explanation, the Kremlin first merely said he had a cold. Later, it indicated he had some illness from which he was recovering.
In the West, such a prolonged absence with no real explanation would send stock markets plummeting and political fortunes skittering up or down. The press would chronicle the event in minute detail.
Not here in the Soviet Union. On the surface, at least, things go on pretty much as they did before Yuri Andropov dropped from sight. The stores and buses are still crowded, the government keeps right on functioning - and the official pronouncements are as cloudy as ever. The press says next to nothing about the leader's health.
But some Western analysts believe that, below the surface, there is a churning - and perhaps the first stages of an incipient power struggle among would-be successors.
''I think (Andropov's absence) is probably as unsettling to Soviet citizens as it is to the rest of the world,'' a senior American diplomat says.
He continues, ''If it looks as if there may be a change in leadership, all sorts of people go scampering around to form coalitions.''
But analysts warn not to assume that a change of leadership is imminent. Until a clear successor emerges, the American diplomat says, ''There is no reason for anyone to want to have a succession. . . .''
There's something else to keep in mind: Stories about the deteriorating health of Mr. Andropov's predecessor, Leonid Brezhnev, were being printed at least seven years before he eventually passed on.
So, for the time being at least, the West must deal with Yuri Vladimirovich Andropov.
There are a few facts known about him. In June, for example, he will be 70 years old. He was ambassador to Hungary from 1954 to 1957, and he apparently played a key role in engineering a Soviet military invasion of the country to put down a popular rebellion. For 15 years, he served as head of the Soviet Committee for State Security, the KGB.
He has been a loyal worker in the Communist Party, finally ascending to the ruling Politburo (as a candidate member) in 1967 and attaining full membership in 1973. He has never visited the West. And his son says he speaks passable English.
From there, we enter the realm of opinion and speculation. And the path is tortuous, indeed.
Various published accounts have described him as an amiable man who dabbles in writing poetry and has been known to lead his dinner guests in singing. An American diplomat who spent time with him found him a bit distant.
Claude Cheysson, the French foreign minister, found him ''lacking in human warmth,'' a ''nonromantic'' who ''works like a computer.''
Even if Andropov himself acts with computerlike efficiency, the same cannot be said about the bureaucracy he heads.
Its first major test in the foreign policy arena gave the world a glimpse of a Kremlin in disarray. The result was a major setback for Moscow, and the handling of the matter plunged East-West relations to their worst point in decades.
The incident was the shooting down of Korean Air Lines Flight 7, and the resultant loss of 269 lives. For six days, the Kremlin denied the incident took place. Then, confronted with overwhelming evidence to the contrary, it justified the action by arguing, without substantiation, that the plane was on a spying mission.
There was no repudiation of the military for having shot the plane down, no apologies were given, no compensation was offered.
A senior American official says the Kremlin's handling of the incident ''will have repercussions for years to come.''
The refusal to censure the military - along with the unusually prominent role the military took both during the incident and in its aftermath - has fueled speculation of rising military influence within the Kremlin.
The proferred reasons? Either that Andropov owes his own ascension to power to the support of the military leadership and is therefore loath to cross swords with them - or that the military has helped itself to a greater share of power while Andropov convalesces.
The Communist Party leadership here dismisses both views. Suggestions that the military is growing in influence ''have nothing to do with reality,'' says a member of the powerful Central Committee.
''They (the military) play their traditional role. In our system, all spheres of political and government activity are being guided by the party.''
Still, Western analysts have their doubts. They indicate the military is, indeed, growing in influence. Some analysts here believe that during a portion of September, Andropov was almost totally incapacitated by illness.
In his absence, they say, a ''collective'' within the Communist Party Politburo wielded power. And this collective, they say, was apparently headed by Defense Minister Dmitri Ustinov.
President Reagan says he finds the situation disturbing. In an interview with Time magazine, he said military leaders ''without any coaching or being briefed by the civilian part of government'' have been ''going public with attacks on the US and seeming to enunciate policy on their own.'' One Central Committee member dismisses such comments as uninformed. But another admits his country can hardly afford to ignore the world's other superpower.
However, a third member argues, ''While Reagan's in the White House, we shall not come to any serious agreements.'' Besides, he continues, ''Domestic politics are more important to us than international politics. The domestic situation forms our base.''
But that does not mean the internal politics in this country are unrelated to Soviet foreign policy - and, therefore, unimportant to the West. The most important domestic political concerns here are economic. A Soviet Union with a robust, booming economy would be a very serious competitor with the West, according to Western analysts.
But as long as the USSR is shackled by its own economic problems, these analysts add, it does not present much of a model for other nations - and therefore presents less of a challenge to the West.
Consequently, they say, there is a direct relationship between the Soviet Union's economic performance and its standing in the world order.
''The Western world and a lot of the third world is moving up,'' says a Western diplomat, while the Soviet Union is stalling and, in some respects, falling behind.
Mr. Andropov, former head of the Soviet Union's espionage network, is undoubtedly aware of the stakes. He came into office vowing to forge changes in the Soviet economy. He sent militia into the shops, stores, swimming pools, and bathhouses of cities like Moscow, cracking down on people who should have been at work.
In speech after speech, he has called for more discipline, management reform, and new approaches to economic development.
Asked what the Soviet Union's top priority is in the year ahead, the Central Committee member replied, ''We are interested in strengthening the positive aspects of the state economy.''
''To move further as a society, it's necessary to change the economy,'' he adds. ''But what levers should be used? This is one of the main questions confronting the modern economy.''
Another Central Committee member confirms that ''the restructuring of the economy'' is the major job facing Andropov.
''We tried to do it in 1965,'' he says, referring to a short-lived attempt at major economic reform.
''But,'' he adds, ''we didn't do it to the end.'' (Western analysts say the entrenched management and planning bureaucracy torpedoed many reforms pushed by Nikita Khrushchev in the preceding few years.)
Will Andropov be any more successful?
''Let's hope so,'' the Central Committee member says.
But Western analysts have a different view - suggesting that the first year of the Andropov era has proven to be a major disappointment.
They note that the bulk of the economic reforms that took effect on Jan. 1 are limited to only a few ministries and a few plants. And these initiatives are simply not enough to make much of a difference in this country's sprawling economy, these analysts say.
When Andropov took office, a senior American diplomat says, ''there were really high hopes for reform, for big change, for doing things better, for getting away from the stick-in-the-mud way of doing things. . . .
''Here we are, a year later, with not that much of a change.
''He's not been able to do what he wanted to do, or what his friends said he wanted to do. . . .''
And some Western analysts say his health problems have complicated matters.
If a leader looks as if ''he will be around'' to demand fundamental change, the American diplomat says, ''you'll really put your back into it.'' But, he adds, ''that is not the case today.''
Soviet officials hotly dispute such analyses. ''Nothing changes when Andropov is sick,'' a Central Committee member says.
''There is a Politburo. There is a system. Things will continue, whether Yuri Andropov is in the Kremlin or in his dacha (retreat).''
Some Western analysts would agree, though perhaps for very different reasons. Indeed, they argue, it is the system itself that virtually guarantees continued economic problems for the Soviet Union.
''You cannot have a major civilian economy run from a central point,'' the American diplomat says, ''but that is central to their doctrine. And they won't change their doctrine.''
Not so, retorts a Central Committee member.
''We are not so narrow-minded to measure all organizational methods against Marxist-Leninist philosophy,'' he says. Besides, that philosophy ''provides for a much wider framework than many in the West believe - even than many Soviet managers believe.''
Andropov, he adds, is committed to freeing the ''vast reserves, huge reserves'' in the Soviet economy. ''This is the central part of his program,'' he adds.
Indeed, there are some positive signs in the country's economy. Soviet industrial production was up by 4.1 percent during the first 11 months of 1983, one of the best rates in years. Soviet meat production appears to have set a record in 1983.
Some Western analysts say there is so much slack in the Soviet economy that even a modest increase in discipline among the workforce can produce such changes.
And the weather is credited with helping farms to grow more fodder, which results in more meat. But, these analysts say, some changes may be of only a temporary nature and are, quite literally, as changeable as the weather.
Andropov does not see it that way. ''People have begun putting more heart into their work,'' he wrote in an address to the Central Committee in late December. ''The rates of economic growth have increased, and quality indicators have somewhat risen. In general, a change for the better in the national economy has begun to show.''
Andropov would have said that to the Central Committee in person, had he been able to attend. But he wasn't. ''Temporary causes'' kept him from taking up his position at the head of his party and his country.
''To run a country like this, from a central point, is a backbreaking job,'' says the American diplomat. ''It takes very vigorous people to do it.''
Is there any evidence that Andropov is not performing the job?
''We don't know.''
Any evidence that he is?
''No one knows.''
Therein lies perhaps the biggest challenge facing Yuri Andropov, the country he leads, and those who must deal with it. For, as the American official concludes, ''Anything that causes uncertainty at the top of their government is not in our interests.
''It is in our own interest to have a stable kind of leadership that you can deal with. . . . We may not agree with them, but at least we can deal with them.''