Mayor Maurice Ferre won a sixth consecutive two-year term tonight after a bitter campaign highlighting ethnic tensions between this city's assertive Cuban majority and an increasingly resentful black minority.

"I think it's been a tough campaign," Ferre said shortly after his challenger, Cuban-born Xavier Suarez, telephoned to concede. "But it's important now to heal the wounds and bring this community together."

Final unofficial returns in the nonpartisan balloting gave Ferre 36,096 votes to 29,747 for Suarez. The victory dashed for another two years Cuban-American hopes of governing Miami directly for the first time since exiles from the island turned the city from a sleepy southern resort into a regional center for Latin America.

Election officials said the hard-fought campaign brought an unusually high voter turnout, particularly in Cuban and black neighborhoods. Overall, the officials said, about 60 percent of Miami's 106,400 registered voters showed up at polling places.

Slightly more than half turned out for last Tuesday's first round, in which Ferre got only 201 more votes than Suarez, leaving the two statistically tied at 42 percent.

Ferre said at a victory celebration tonight that one key to the outcome was the high turnout of black voters, generally considered sympathetic to the mayor. He also credited what he said was voter backlash against a last-minute turnabout by City Commissioner Joe Carollo, who unexpectedly announced support for Suarez during a news conference called by Ferre.

"It wasn't my style," Suarez said tonight of Carollo's maneuver. "Apparently, a lot of people didn't like that."

Ferre, 48, is of Puerto Rican ancestry and speaks Spanish. But he sought particular support from Miami's blacks, winning endorsements from the city's top black leaders and campaign assistance from Mayor Andrew Young of Atlanta.

Suarez, 34, a resident of Miami's Little Havana district, lost two earlier races for the City Commission. The Harvard-educated lawyer pitched his mayoral campaign toward the 60 percent of the city's population that is Hispanic, overwhelmingly Cuban and predominantly white. Palm cards prepared by his supporters urged, "Cubans, vote Cuban."

In separate appearances and head-to-head debates this past week, Ferre and Suarez defined sharply different visions of what kind of Miami they stand for, aside from the question of Cuban power.

Ferre, a builder who over the last 10 years has encouraged Miami's swift downtown growth, insisted that becoming "Manhattan South" would not be a bad thing for the city. He said $3 billion in recent construction has turned Miami into a big city, and "the issue before us is what kind of a city Miami is going to be in the year 2000."

"That spectacular growth has given us the revenues by which we can increase our services," he said last night in a final campaign appearance.

Suarez, who has not held public office, charged that Ferre overemphasized downtown growth at the expense of neighborhood services. He proposed local police precincts, police foot patrols and a $5 million jobs program that he said would provide salaries for 400 unemployed.

Talk of urban issues was drowned out, however, by mutual recrimination and accusations of playing to ethnic strains. The Miami Herald, under the headline "Shameful Campaign," editorialized Saturday that both campaigns deserved condemnation for their bitter tactics.

One particularly intense moment came when Carollo, a Cuban, appeared at a news conference called Thursday by Ferre for what was expected to be an endorsement. Instead, Carollo stunned the mayor by denouncing him for conducting "a racist campaign of hate." Ferre complained he was the victim of a "political ambush."

Les Brown, a commentator on the black-oriented radio station WEDR, urged blacks last week to get out and vote to head off a "Cuban takeover" such as he said happened in nearby Hialeah.