After one of the memorable events in which he played a leading part, Mr. Justice Oliver Wendell Holmes was moved to a bitter comment about the ignorance of press analysis over his role. It struck him, he said, that many people "writing with the sanctity of newsprint" didn't appear to know a damn thing about his opinions.

To someone who had worked so hard, as he put it, "to make every word live," this lack of understanding of his work was particularly galling.

Let the great Holmes' concern serve as a proper warning.

Readers searching for fresh insights into the inner workings of the Supreme Court and its justices -- the "supremes," as we breezily (and privately) call them on this paper -- in view of the latest news about the court will have to look elsewhere than here.

As Mr. Justice Potter Steward said in a rare news conference Friday inside the court, trying to understand fully how the justices reach a decision is akin to an outsider gazing down on a complicated operation in a surgical amphitheater. When it's over, you can tell whether the patient survived but not how the surgeon accomplished his art.

Caveats aside, that doesn't mean an outsider can fail to miss the significance of the change now upon the Supreme Court -- a change that comes at a historic moment with a potential affect American society for the rest of this century and beyond.

Luck as an element in the fortunes of public leaders, and in their ability to forge public policy, cannot be overestimated. Ronald Reagan is exceedingly lucky.

His luck is twofold. He stands today in a position to reshape the Supreme Court as profoundly as an president since Franklin Roosevelt -- and his opportunity occurs at a time when his own popularity, always a fragile commodity for a president, probably has reached its peak.

Already there are signs that point to an inevitable erosion in Reagan's present high standing. Last week's news conference, his first since he was shot, rates as the clumsiest such presidential performance in memory; any further examples of disturbing lack of preparedness and an inability to deal effectively with critical questions almost certainly will affect his standing. Ahead lie the hard political battles that will be fought as the realities of his budget slashings reach the public beyond Washington. When that struggle finally is fully joined, as it has not yet been, he is bound to lose some of his political credit -- and his power to work his will.

Thus, the timing of the first Supreme Court vacancy in six years becomes even more important. For Ronald Reagan, the earlier the chance to fill that slot the better the prospects to get what he wants. This president, even more than most, wants a lot.

Reagan, is fortunate in another respect, and this largely of his own making. His political skills and his popular appeal carried other Republicans to power with him last fall. In terms of his Supreme Court appointment, it will fall to the first Republican Senate in a generation, cast in a far more Reagan brand of conservatism, to exercise the historic power to advise and consent to his court choice. How great a shift has taken place hardly needs underscoring; but it's difficult to imagine amore dramtic ideological sea change than Strom Thurmond instead of Edward Kennedy presiding over the Senate Judiciary Committee's forthcoming deliberations over Reagan's nominee.

History has accomodated Reagan in another way. The successive shocks, whether of sudden death, disgrace, or defeat, that have torn at American presidents for a generation now have resulted in an anamoly concerning the court. While the Democratic Party has controlled the federal government for almost half a century, the present composition of the court derives from Republican selection.

Only two of the nine sitting justices were appointed by a Democrat, and the last such, Thurgood Marshall, ascended to the bench 14 years ago. Potter Stewart's resignation leaves five justices at age 72 or older. The prospect for Reagan to appoint as many as six justices in his term therefore stems from something more than feckless speculation. Leaving aside George Washingtion, who as the first chief executive named all nine justices, in our history only one president -- FDR, with eight -- appointed as many as six to the highest tribunal.

These circumstances alone add significance to Reagan's choice. But something more fateful is at stake. Reagan's first court nominee comes at a time when a historic debate about the nature of the federal government and its relationship to the states and local communities is under way. It is Reagan's political promise to alter those relationships fundamentally. Nothing is more critical to the outcome of that struggle than the role of the federal courts in the federal system.

Initial comment over the kind of person Reagan will choose for the court has revolved around whether he will name a woman. For many reasons it's more than time, of course, for a woman to serve as a Supreme Court justice, but something far greater than sex is at stake. The principal question concerns ideology.

Last summer in Detroit, the Republican Party adopted this language in its platform:

"We will work for the appointment of judges at all levels of the judiciary who respect traditional family values and the sanctity of innocent human life."

If Reagan applies that sort of standard to the Supreme Court we will have entered a radically different stage of our history, one in which ideological conformity becomes the operative norm.

In his farewell news conference Friday, Potter Stewart gave eloquent voice to another standard. It is the old one, fashioned painfully out of two centuries of experience at attempting to safeguard individual liberties and the rights of citizens to be free to differ in thought and action. Philosophically, that was the essence of what Chief Justice John Marshall called the need to have a "well regulated democracy" in which the Supreme Court he helped create has played so vital a role.

Stewart was asked what part ideology should take in the deliberations of a justice. "It is the first duty of a justice," he said, "to remove from his judical work his own moral, philosophical, political and religious beliefs and not to think of himself as some great philosopher king and apply his own ideology."

Peering down on him as he spoke was the solemn portrait of John Marshall, and hovering in the marble corridors was the spirit of old Oliver Wendell Holmes. If they could, they would have been cheering at that expression from so worthy a successor. Who knows? Perhaps they were.