Dutch Morial, this city's first black mayor, won an easy reelection Saturday by keeping a virtual hammerlock on the black vote and putting together a coalition of diverse segments from the rest of the city.

Morial, 52, received 100,725 votes, or 53.2 percent. State Rep. Ron Faucheux, 31, who is white, got 88,573, or 46.8 percent. These unofficial totals, which will be certified later this week, do not include about 2,300 absentee votes.

Morial had won the first vote--an "open primary" with six candidates on Feb. 6--but by a much closer margin, 46.9 percent to Faucheux's 45.4 percent. Both men are Democrats.

In campaigning for the city's top job, Morial spent about $1.6 million, and Faucheux spent about $1.2 million.

Morial, who has legally changed his name from Ernest to his childhood nickname, was supported by most of the business establishment, labor unions, a former Mardi Gras king and New Orleans' gay political action group.

Faucheux won the endorsements of the Community Organization for Urban Politics, a black group better known as COUP; state Sen. Henry Braden IV, one of the state's two black senators; and former mayor Moon Landrieu, Morial's immediate predecessor and the first mayor to appoint blacks to decision-making posts.

But these endorsements did little for Faucheux--or for Braden and Landrieu. Braden reported receiving obscene telephone calls, and he said his car was spray-painted white. Landrieu, who was secretary of housing and urban development in the Carter administration, was booed when he addressed the state Democratic Party convention after endorsing Faucheux. Some delegates walked out.

In Saturday's voting, several pollsters said Faucheux, who had received 1 percent of the black vote in the first primary, was unable to raise that total to the 5 percent he was hoping to attract.

Blacks make up 46.3 percent of New Orleans' 253,593 voters. Saturday's fair, warm weather was believed to have favored Morial because poor blacks, part of the mayor's natural constituency, could walk to the polls.

Citywide, the overall turnout was nearly 75 percent, but the percentage of black voters was believed to be higher than the percentage of white.

In 1977, Morial won with about one-fifth of the white vote, and in the February primary, he received about one-sixth. He wooed the white business establishment by citing the building boom, due chiefly to good times in the petroleum industry, which had created about 9,000 private-sector jobs during his term. He also campaigned on his scandal-free record and elimination of unnecessary expenditures, equipment and jobs.

Businessmen pumped money into his campaign and signed newspaper advertisements for Morial, and Brooke Duncan, who once reigned as Rex, King of Carnival, did a television commercial for him.