In Rockefeller Center, scaffolding rises around the towering Christmas tree and skaters below circle happily on the rink. On Fifth Avenue, the shoppers are out, their pace brisk, while bands of musicians play and sing on street corners. The season has begun and, as always at this time of year, in this section of Manhattan, all seems well. Good tidings again.

By all normal measurements, this should be an assured time for Americans. We've come through the longest, most exhausting political contest in our history without, it seems, leaving behind the kinds of bitter legacies that so often mar those struggles. The sense of a new beginning -- a new president to lead the nation into a new decade -- appears strong. People you meet express, it not a form of euphoria about the prospects for the next president, at least a generalized hope that he and his people will do better. And this fresh start takes place without the ugly recriminations from an unpopular war or historic scandal that greeted other recent new presidents. The possibility of entering a welcome period of national good will certainly exists.

But strangely an undercurrent of anxiety, of nervousness, of ill-defined but nonetheless real fears about the future also appears to be present. Part of this is inevitable: the first rush of enthusiasm for the great Reagan victory that sent the stock market soaring to new highs has ended. Now, some of the same people in New York's financial houses who reacted so emotionally to the election news are taking a more tempered view. They still hold high expectations for the new administration, but the initial dreams for some golden era of prosperity soon approaching have largely disappeared. As an analyst for a major investment house puts it, Wall Street will have to recognize that the Reagan plans to cut taxes and increase defense spending substantially are inherently inflationary.

This realization comes even as interest rates again are rising to the near-record levels of last spring and the general economic outlook seems dismal. In the hard second look now taking place in business circles here at what a Reagan presidency can achieve, you hear serious questions raised about the realities of assuming power today -- and doublts whether the new administration, no matter how well intended or even well staffed, will be able to accomplish its goals. An appreciation of the difficulties of carrying out the presumed mandate of slashing government waste and cutting through government red tape and eliminating stultifying government regulations is clearly present now to a greater degree than before the election.

Beyond this exists a general feeling that hard times may well be ahead for the country and that the new president will face formidable obstacles even in matters over which he presumably has control. Far more serious and troubling are the problems beyond his immediate control. They are contributing mightily to the present uneasiness intruding on the good will of this holiday season. Principal among them are the events in Poland.

In the present quietus that envelops the transfer of power in Washington, when the government hangs in limbo, decisions are deferred, and the new president waits in the wings a continent away, the Polish crisis has crept ominously upon us. The dramatic and heartening story of Poland's courageous struggle for freedom has been with us, of course, for many months, but the new developments seem to have taken the general public by surprise. That was not true of high officials in Washington; a few days after the election, for instance, someone told this reporter of concerns that Russia might invade Poland sometime in mid-December (he even picked a hypothetical date of Dec. 13), an act that would have profound implications for world peace and U.S. Soviet relations for the rest of this century. But in the understandable preoccupation with the presidential campaign and its startling results, the dangerous turn in Poland did not command major public attention.

It's not too much to suggest that the threat posed in Poland is one of the gravest since World War II. If the Russians decide to crush the Poles with armed force -- short of declaring war, realistically the United States could do little about that decision -- they will have done more than demonstrate anew their fears of tolerating any democratic impulses from within their sphere of influence. They will have thrust back their relations with the United States to a level even worse than the Cold War period, back to the time before we recognized the Soviet Union. The official American position then was articulated forcefully by Charles Evans Hughes, our taciturn and distinguished secretary of state in the early 1920s. When Samuel Gompers, the head of the American labor movement, raised questions about recognizing Russia, Hughes coldly responded:

"The sentiment of our people is not deemed to be favorable to the acceptance into political fellowship of this [Soviet] regime so long as it denies the essential basis of intercourse and cherishes as an ultimate and definite aim the destruction of the free institutions which we have laboriously built up."

Now, in this infinitely more dangerous decade, the question of Soviet-American relations goes far beyond political friendship. Nothing less than survival appears at stake. Not the cheeriest of omens for this happiest of times.