So they think the common cold might be conquered. Why not? In this age of astonishing medical and technological advances, of artificial hearts and floating space satellite systems, one wondrous discovery swiftly supplants another.

But I rise here to note not the latest scientific miracle but one of the natural marvels of our times, Ronald Reagan.

In a week Reagan begins his sixth year in the White House. Two weeks later he celebrates his 75th birthday -- and a jauntier, spryer septuagenarian we've never seen in public office. Age, burdens of the presidency, an assassin's bullet an inch from the heart and even major cancer surgery seem to have left no marks on him. Physically, he continues to exude well-being and vitality, charm and commanding presence. Politically, he continues to confound his critics, including this one.

His news conference the other night was the latest case in point. He was defensive, he stumbled over his prepared text, he misstated facts, but, as usual, in the end he prevailed. And after a great deal of floundering about (with accompanying harsh Reaganesque rhetoric) over what course to pursue against terrorism in Qaddafi's Libya, as usual, in the end, he chose the proper, more moderate one.

This has been the story of his presidency so far. He leaves his liberal and conservative critics sputtering that he's either too ideological or not ideological enough, too harsh or too weak. Yet he continues to steer his own course, and continues to demonstrate a capacity for flexibility that is the hallmark of effective leadership.

He'll need all of that flexibility and political presence in this year of great testing ahead. For him and for the second session of the 99th Congress, 1986 promises to be wrenching and volatile. Major issues remain unresolved: whether to raise taxes, reform them, do both or neither; how to get deficits under control without creating governmental and public chaos; how best to pursue the new beginning with the Soviets and achieve an arms control agreement while questions about the "Star Wars" antimissile defense system remain unresolved and the Libyan-Soviet connection creates new superpower tensions.

And all this takes place amid a high-stakes election year that holds unusual significance for the future of both political parties as they begin to look beyond the Reagan era.

But whatever the outcome of these and other questions, and however flawed some of his policies may be, Ronald Reagan's presidency already has accomplished something of great -- and possibly lasting -- importance. He has restored the office of president of the United States to a position of power and prestige. He has demonstrated that, no matter how difficult the issues or divided the political process, a president can lead and can achieve political success.

That's easy to say now, but five years ago the climate was far less conducive to strong presidential leadership. A sense of despair, of impotence, of frustration, permeated the political process. After a succession of failed presidencies, a feeling of instability had begun to surround the office. The range and complexity of problems appeared beyond the capacity of any person who became president.

And not only the presidency was seen as failing; the American political system seemed unstable. I was not alone in expressing concerns about what appeared to be our inability to govern. Scholars and statesmen began to ask whether fundamental constitutional changes, such as a single six-year presidential term and a four-year one for members of the House, might not be desirable. They still do, but without the urgency that prompted the calls then.

Almost by sheer will of personality, by the effortless exuding of confidence, Reagan has reversed much of that feeling. The presidency is a stronger office today because of him.

So, Mr. President, some of us may not like many of your prescriptions. We may passionately believe certain of your doses to be dangerous. Certainly we don't think you have a cure for all that ails us. But that doesn't stop us from admiring the way you administer your medicine. And when it comes to personal leadership qualities, whatever brand it is you bear ought to be patented as a national treasure.

NOTE: On Sunday before Christmas, I reported here on the plight of more than 30 Afghan refugees who were being held in an immigration service "detention center" in New York for lack of proper documents or visas upon entry to the United States. They already had been held there for many months and faced the prospect of incarceration for as long as three years before learning whether they would be granted asylum in this country. Their crime, if any, was the crime of seeking asylum in a country that prides itself as being a haven for political dissidents -- and a country that has been aiding the same Afghan rebels in their fight against Soviet troops in their homeland. They deserved, as I wrote then, the gift of freedom. I am pleased to report that on Friday they were all freed after the personal intercession of New York Sens. Daniel Patrick Moynihan (D) and Alfonse M. D'Amato (R) and Rep. Gary L. Ackerman (D).