Ernest N. (Dutch) Morial was elected New Orleans' first black mayor Saturday by winning virtually every black vote and increasing his share of the white vote.

Morial, 48, defeated City Councilman Joseph V. DiRosa, 60, a white, by 89,823 votes (51.57 per cent) to 84,352 votes (48.43 per cent in unofficial returns of 2 runoffs in which 76.1 per cent are black, and Morial received between 97 and 98 per cent of these votes, according to spot checks of heavily black precincts.

Morial, who resigned his stake appellate judgeship Nov. 4 after a federal court ruling threw in his eligibility into doubt, scored well in the dominantly white areas, getting as much as 40 to 45 per cent of the votes in some of these percincts, primarily in uptown New Orleans, in liberal areas near Tulane and Loyola universities and in the Garden District, where many of the city's "establishment" live. His low-yield areas were in the expensive conservative subdivisions along Lake Pontchartrain, where he received 10 to 12 per cent of the vote.

Overall, poll reports showed that he captured roughly 19 per cent of the total white vote - up from 7 per cent in the primary.

"That I received a representative number of votes from the white community is indicative of the character of this city," Morial said today.

He will be sworn in next spring, succeeding Mayor Moon landrieu, who was barred by city law from seeking a third four-year term. Morial will become the black elected official with the largest constituecy in the South, surpassing Maynard Jackson of Atlanta.

Throughout the campaign, Morial's chief issue was fiscal intergrity. He said some sort of additional tax - posibly a metropolitan earnings tax - saying that more levies would not be needed to continue to provide city services.

However, the principal issue was Morial himself - first, his race, and, toward the end of the campaign, his eligibility to run.

Morial's career has been a series of "firsts." The first black graduate of Louisiana State University Law School, he became in 1967 the first black member of the Lousiana Legislature in the 20th century. Three years later, Gov. John J. McKeithan appointed him a judge of the Orleans Parish (county) Juvenile Court, and in 1972 Morial won a seat on the Fourth Circuit Court of Appeal, making him the highest elected black in the state.

However, in 1969, DiRosa defeated him for an at-large City Council seat.

Though he was often a "first," Morial was no firebrand.

In the legislature, while he voted to get rid of some of the state's Jim Crow laws, he proved to be an average legislator who was concerned with getting state rewards for his district and for the Port of New Orleans, this city's main industry. He is married and the father of five.

In the 11-candidate Oct. 1 primary, race was an implicit issue, but during the runoff it broke into the open.

DiRosa accused Morial of importing out-of-state blacks to register to vote, and, in a conversation with a reporter that was later corroborated by a witness, referred to blacks as "jungle bunnies."

DiRosa also ran a newspaper as attacking U.N. Ambassador Andrew Young, a New Orleans native who had backed Morial in an interview here.

But the racial issue paled during the last nine days of the campaign, when Morial's candidacy was thrown into doubt by a federal court.

Morial resigned his judgeship after an adverse ruling Nov. 3 by the Fifth U.S. Circuit Court of appeals on his challenge to a state law which prohibited judges from running for non-judicial offices.

On a lesser level, DiRosa's personality was an issue because his positions on the City Council and rankled "establisment" New Orleanians, and he had been a consistent foe of New Orleans Public Service, Inc., which furnishes electricity, gas and tranist services, and the city's sewer and water board.