Writing de profundis to a Kennedy presidential promise has become a ritual act for a generation of American journalists, so one more time hardly counts as original. We have, political season in and out, preached over the fallen Kennedys, one by one, consigned them to the past and then turned to the next in line. With the last of the brothers, Ted, the exercise has become so commonplace that it now rates as little more than a one-day wonder. Quick flash, quick dismissal.

As my colleague Albert R. Hunt of The Wall Street Journal points out, Kennedy now has taken himself out of a presidential race for the fourth time in five elections. Still, speculation continues about the eventual, conclusive Kennedy presidential race that finally will take him into the White House.

I believe that can now be discarded.

Sure, Edward M. Kennedy might yet become president. He says he still wants to be, and therefore he must be considered a possibility later. Recent history abounds with repeated examples of supposed historic losers who nonetheless became president, and, yes, 24 hours remains a long time in the life of a politician.

Three of our last five presidents -- Lyndon B. Johnson, Richard M. Nixon and Ronald Reagan -- unsuccessfully sought the White House and consequently were written off by the political handicappers of the press. So perhaps Kennedy will join their ranks six or 10 or more years hence. Anything can happen.

But with Kennedy, that now stands as unlikely. More important, his latest withdrawal from consideration has, in my view, truly written an end to the continuing Kennedy dominance or, depending on one's point of view, stifling of Democratic presidential politics.

Only once before has the Democratic Party been so singularly dominated by one name for a comparable period of time. In the late 1880s, William Jennings Bryan began what became a 30-year span in which he dominated the Democratic nomination process and articulation of Democratic issues. Three times in that period he became his party's nominee.

Although he lost every race he entered from an 1894 Senate contest on, his prestige and influence were so great that he was able to throw his party's support behind a candidate who finally broke the long years of Republican rule, Woodrow Wilson in 1912.

But Bryan never dispensed the sort of real political power that the Kennedys collectively have exercised for nearly three decades through control of the White House, their Senate seats, their formidable national political network and, in this media age, the ceaseless glare of the public spotlight on them.

For years, since John F. Kennedy decided to go for the presidency after losing the open vice presidential contest at the 1956 nominating convention in Chicago, every Democratic race has revolved around the name of Kennedy. Each contest was shaped by the Kennedy factor, for brother after brother after brother.

Whether it was Kennedy candidacy, Kennedy challenge or Kennedy withdrawal, the Kennedy presence hung over every presidential period and affected every candidate, declared or not. In the process, it kept some prominent Democrats, who might have won, from running and permitted others with nothing to lose to take the longshot gamble, win the nomination (George McGovern) and even the White House (Jimmy Carter).

Now that continuing story is over. The logjam has been broken. At the least, Kennedy's current self-removal from the race liberates the Democratic Party.

It quite likely liberates Kennedy himself. For a generation he has been at the center of the extraordinary pressures and problems, public and private, that have been the Kennedy family's fate. Now, at last, he is free to pause, to draw a different sort of breath, to reexamine the life, political and otherwise, around him.

The question is what Kennedy and the Democrats make of their new condition. Both are in a position of having to define more clearly what they stand for in the face of changing political times and issues. Each has a new role to play.

For Democrats, the immediate political period presents opportunities and even greater challenges. They must fashion coherent alternatives to Reagan approaches at home and abroad. They must demonstrate that they have practical ideas about the critical and, in terms of forging workable policies, contradictory issues facing the country: defense and jobs, entitlements and the enormous rising budget deficits. Most important, they must show they are capable of fresh thinking on one issue, Social Security.

It is not too much to suggest that the credibility and perhaps future of the Democratic Party rest upon how well it handles the Social Security question. It is the Democrats' program, the quintessential governmental commitment to keep older Americans, whose ranks grow ever larger in our society, from finishing their years without even the ability to purchase food and provide shelter.

But Social Security today stands in serious trouble. Its problems are going to become worse. Now the burden falls on Democrats to look at the social side of the public ledger that is so much their creation and move on Social Security.

For Kennedy, the challenge lies in other areas. His problem is not in discarding liberalism but in redefining it for America in the 1980s and beyond. As much as anything else, that means redefining the role of the federal government.

Obviously, approaches of the New Deal days are not adequate to this present and future. As our industrial base changes dramatically and perhaps permanently, so do the nature and quality of work. America stands at the center of a world economy of increasing fragility and interdependence. No amount of wishful thinking or nostalgia for a simpler day will permit the role of the federal government to become less.

The latest unemployment figures alone, showing a dramatic monthly increase and 12 million Americans out of work, underscore the federal role that must be played in alleviating that distress immediately and in creating retraining programs for a different kind of employment base. That federal role is certain to be greater in the years ahead.

As America enters a period of strain and tension in a transition to a different future, the test is how to fashion a practical and compassionate government that attracts the nation's best talents to serve it, that restores the tattered concept of public service to its proper place of respect, that looks at problems with a hard eye of realism but also with a recognition that government has an obligation to help those unable to help themselves.

Ted Kennedy and the Democrats now have an opportunity to show how well they are up to meeting these new leadership roles and challenges.