Boston and Miami

The mayoral elections of City Councillor Ray Flynn in Boston and incumbent Maurice Ferre in Miami once again underscore how unique and individual US cities are. And both elections show how important coalition building has become in America's cities, where scores of new immigrant groups, young professionals, lower-income persons, and the elderly are replacing traditional ethnic and working-class neighborhoods.

In Miami, Puerto Rican-born Mayor Ferre was returned to office for a sixth term by forging a coalition of blacks, whites, and some Cubans. His opponent, Xavier Suarez, is a Cuban-born lawyer. The often-acrimonious contest was fought out along racial lines.

In Boston, Ray Flynn captured a surprising 66 percent of the vote in turning back opponent Mel King's bid to be the city's first black mayor. Mr. King had run on a ''rainbow coalition'' that sought to encompass blacks and moderate whites. The Boston election was a cleanly fought contest. Both candidates stressed a need to revitalize the city's neighborhoods.

For Mr. Flynn, the first mayor-elect in the city's history to have come from largely Irish South Boston, scene of strident anti-busing opposition a decade ago, the task is clear. He will have to reach out to all Bostonians ''with unity and pride,'' as he said Tuesday night. One quid pro quo would seem to be admitting some King people into the new city administration.

For Mel King and the ''rainbow coalition,'' meanwhile, there should be no sense of defeat. As shown in other cities, black candidates generally lose in their first citywide bid.

As Mr. King himself acknowledged, his very success in winning a primary slot showed that ''the city of Boston has taken a giant step forward.''