Still two years before the next presidential election - and suddenly the political scene is crackling with excitement. Why? Ironically, because front-runner Ted Kennedy has chosen not to run. The Senator's timely - and wise - decision means the field is now wide open to new candidates and new ideas. The Democratic Party, bolstered by its recent electoral successes, confronts an opportunity for renewal that should benefit the entire political process.
We say a ''timely'' decision because Mr. Kennedy has courteously given his fellow Democrats the advance notice they need to make their own political plans. We say ''wise'' because, for all his political strengths, Senator Kennedy also had a major liability. It is hard to know what factors - family duties, concern about assassination, Chappaquiddick - weighed most in his decision. But the fact that his aides ran ''character ads'' during the Massachusetts election campaign indicated that the morally damaging episode on Martha's Vineyard remained a political question mark. Indeed, while many Americans are tired of the subject, and ready to leave it behind, it is far from certain that it would not have surfaced to defeat Mr. Kennedy in a race for the nation's top job.
The decision was wise on another score as well. Mr. Kennedy can be a more valuable public servant now that he is out of contention and can stand aside from the intraparty maneuvering. Not that the senator has removed himself from future presidential ambitions. He is a relatively young man and - by the standard of today's officeholder - he could go after the White House in any of four other future elections, even in the year 2000. Knowing the Kennedy political staying power, it would be foolish to rule out anything.
In any case, other Democrats will now be coming to the fore. Some names already are known. Leading them, of course, is Walter Mondale, an attractive candidate who nonetheless carries the baggage of his association with Jimmy Carter. Then there's John Glenn, the senator from the key state of Ohio who seems to be out front at the moment as the ''man to watch.'' But there other able candidates, among them former governor of Florida Reubin Askew, Sen. Ernest Hollings of South Carolina, Sen. Alan Cranston of California, and the youthful legislator from Colorado, Gary Hart.
Considering the general decline of the American political parties in recent years, it is encouraging that capable politicians are developing within both the Democratic and Republican camps. Also to be noted are the beginnings of fresh thinking in the Democratic Party. Even before Senator Kennedy's withdrawal from the presidential race, Democrats were searching for alternatives to the old-style liberalism.
What exactly will replace it is far from clear. But many Democrats are prepared to say that the old New Deal approaches to social welfare have run their course and new ones must be found. Not that the Democratic Party will want to abandon its concern about the poor. The challenge will be to evolve social policies that not merely provide material help for those in need but lift them out of a self-demeaning state of perpetual depen-dence. It is perhaps one of the most significant political developments of recent years that so many Democrats have swung toward a more conservative middle-of-the-road philosophy on these questions.
This doubtless will make it more difficult for the Republicans to breeze through in 1984. How the Kennedy decision will affect President Reagan's own calculations is impossible to know (whatever the conventional wisdom that he would certainly run if Kennedy were on the ticket). Mr. Reagan remains in the dominant position, and for political and presidential reasons will make sure he stays there. The country will have to wait a good while before it knows his intentions for sure.
In the meantime the great Democratic debate is under way - and Americans should be ready to listen and participate.