A Voice of the Center

THE announced retirement of Sen. Sam Nunn, a Georgia Democrat who has helped define the middle ground in America, sends some shivers through the body politic.

Senator Nunn has been a force in pulling his party away from the liberalism of the 1960s and '70s. He has been a bridge between the parties in Congress. Prominent Republicans, as well as Democrats, were urging him to stay on.

A raft of other senators have announced they, too, won't run in '96, but few command the breadth of respect that Nunn does.

The senator is best known for his expertise on national security, but his stepping-down speech included sharp warnings about inequities among Americans - especially the plight of those who are not getting the education and experience to compete in the next century.

The senator also warned of the eroding moderate ground in politics. If Republicans and Democrats continue to pull right and left, he said in a TV interview Monday, Americans may demand another party.

The country needs leaders who span the gaps between ''hawk'' and ''dove,'' between liberal concerns and conservative ones. Perhaps the greatest threat facing American political life is a further polarization of politics, leaving a broad midsection of views unrepresented and deepening the cynicism already felt by many.

Nunn's was, and is, the kind of voice that counters cynicism: calm, reasoned, a Southern Democrat with heart and without parochialism. May others pick up his themes.