The most unequivocal reactions to Sen. Edward M. Kennedy's announcement that he would not seek the presidential nomination in 1988 came from opposite ends of the political spectrum.

Edward J. Rollins, the manager of the 1984 Reagan campaign and until recently the White House political director, said, "It takes away the one candidate we were sure we could beat." Jesse L. Jackson, the civil-rights activist and Democratic presidential contender, said, "It removes one of the fingers in the dike, holding back those pushing the Democratic Party to the right."

That people as opposed in philosophy and politics as Rollins and Jackson found reason to lament Kennedy's departure says volumes about the centrality of the place he occupied in 1988 politics.

For 25 years, Democrats have found in the name Kennedy the emblem of their past success and their hope for regaining the winning touch. For 16 years, since Chappaquiddick, Republicans have seen the holder of that name as the symbol of the hollowness of that Democratic dream.

With Ted Kennedy sidelined, both parties now know that the Democrats will be led into the next election by a stranger, and perhaps one -- such as Sen. Joseph R. Biden Jr., of Delaware or Rep. Richard A. Gephardt of Missouri -- who was too young even to vote for John F. Kennedy. That changes the dynamics for both parties -- immediately for the Democrats and ultimately for the GOP.

Jackson's comment defines the Democratic dilemma: Who can hold the party's voter base, which is predominantly among the poor, the minorities and single working women, and at the same time expand its reach into the ranks of middle-class married couples.

Kennedy was the one prospective 1988 contender who could challenge Jackson, at the level of emotion and enthusiasm, for the allegiance of minorities and the poor. That gave him freedom to reach for the middle class, as he began to do this year with his votes on the Gramm-Rudman budget process and other issues. Rollins and other Republicans calculated that Kennedy would ultimately be defeated by "the character issue," which cuts deeply with many middle-class married women, especially among his fellow Catholics. But the very fact that Kennedy abandoned the presidential quest so early suggests how difficult it will be for any Democrat to hold that current party base and expand into the middle class.

Neither Sen. Gary Hart, the presumed front- runner, nor Gephardt nor any of the southern and western Democratic governors and senators who are speculative contenders for 1988 can voice their technocratic visions of a growth- oriented economy and society without being accused by Jackson of turning their backs on the Democrats' most loyal and most needy constituencies. With Jackson clearly contemplating the option of an independent candidacy after the 1988 primaries, the threat of sundering the Democratic coalition is not an idle one.

Biden and New York Gov. Mario M. Cuomo are in better positions, because both of them have won campaigns with heavy minority support (in Wilmington and New York City), and both are, like Kennedy, the kind of orators who can sway audiences in black churches.

At the same time, both Cuomo and Biden have emotional appeals to middle-class families. Cuomo evokes the immigrant tradition of ethnic pride. It lives on in many second-and third- generation Irish, Polish, Hispanic and Italian families like his own, who have achieved success by their own sacrifices and efforts but crave acceptance and recognition.

Biden's appeal is embedded in a classic story of triumph and tragedy. A few weeks after he was elected to the Senate at age 30 in 1972, his wife and infant daughter were killed in an accident. For 13 years he has put his family first, commuting daily between Wilmington and Washington in order to be with his new wife and daughter and his two sons from his first marriage.

At this point, none of the Democrats -- not even previous contender Hart -- commands deep loyalty from more than a tiny handful of his fellow partisans. Most of the prospective candidates are total strangers to the 1988 primary electorate.

The prospect of a political blind date is theoretically an exciting one. But the last time the Democrats nominated a stranger, his name was Jimmy Carter, and the experience was ultimately a disillusioning one. Any satisfaction the Republicans may find in this situation is likely to be short-lived, however. As Rollins said, "It should end our wishful thinking."

The Democratic nominee in 1988 will be someone unencumbered by direct links to the party's checkered recent past. He will be someone who has created his own constituency and defined his own approach in the crucible of a tough nomination contest.

Especially if the Republicans nominate Vice President George Bush or anyone else attempting to provide Reaganism without Reagan, they may find the country ready for something other than hand-me-down leadership.