In their first seriously contested election for local government in more than half a century, voters in the oil-rich toe of the Louisiana boot have exorcised the ghost of late political boss and segregationist Judge Leander H. Perez by electing a black man and a woman.

"The people of Plaquemines Parish are free at last, black and white, for the first time," declared Ernest Johnson, whose 1975 voting discrimination suit paved the way for his election Saturday as the first black commissioner in this swampy parish, or county, of alligators, Cajun fishermen and sawgrass that was once run as one man's fiefdom.

Germaine Curley became the first woman elected to the Plaquemines Parish commission council.

"This means no more dictatorships," said Johnson. "If the judge were still alive, he'd probably swallow his cigar."

Indeed, the new parish council will be without a member of the Perez family for the first time in 22 years. Judge Perez, a multimillionaire from oil and gas leases secured on state and parish lands in the 1930s while he served as local district attorney, retired as council president in 1967 after annointing his younger son, Chalin, his successor. Leander Perez Jr. was already the district attorney.

That was the last year council elections were held at all--until January's crowded primary and Saturday's runoff. Commissioners were picked by the Perez machine and ran unopposed.

A federal court order in Johnson's reapportionment suit halted all local elections until the five-member commission council, elected at-large, agreed last year to expand to nine members, all elected from single-member districts. At-large elections had made it impossible to elect a black in a county with a 25 percent black population.

Saturday's political revolution is the latest chapter in the saga of a Deep South family dynasty. For more than 50 years, the Perez family ruled the parish, the judge's influence reaching into state and national politics.

"These were poor, rural unsophisticated people and an educated person with a law degree like Leander Perez had a big advantage," said historian Glen Jeansonne of the University of Wisconsin.

Perez railed against blacks, Jews and communists, spurned federal aid, keeping power through patronage. With the parish's vast mineral wealth, he ran a virtual welfare state, paving roads, building schools and paying pensions to widows and grants to the college-bound, still parish customs today.

Now, like a real-life Dallas, the patriarch is gone and the sons are fighting over his legacy in what he called "The Promised Land," a parish stretching from New Orleans 120 miles south to the Gulf of Mexico. Although the judge died in 1969, his sons are still referred to as "the children," and their feud opened an avenue for rivals to challenge the dynasty.

Leander Perez Jr., 61, the judge's oldest son and still parish district attorney, is under indictment on a charge of malfeasance. Chalin Perez, 59, a lawyer, did not run again for reelection after being ousted as council chief, then stripped of power last year by renegade commissioners led by Luke Petrovich, 53, a former Perez protege.

Chalin's wife, Lynn Perkins Perez, also a lawyer, was defeated when she ran for the state circuit court of appeals in 1981.

In the Burus town auditorium early today, over spicy gumbo and beer, blacks and whites celebrated the Johnson and Curley victories as symbolizing freedom from bayou political czars. Johnson won a tight race in a predominantly white district with heavy support from white fishermen. Curley, a white, swept to victory.

The two also celebrated a victory against Petrovich, who has emerged as the new parish boss and campaigned against them. Petrovich ran unopposed for his council seat and says his mission is to regain oil lands he says were "stolen" by Judge Perez.

But Chalin Perez, an ex-Navy officer who once dodged "suicide Charlies" in the Pacific, vows that he has just begun to fight. "I have news for them," he snapped. "Chalin Perez will be involved for a long time to come in public life."

No one underestimates the remaining Perez wealth and influence. "Anyone who thinks they're finished is being very, very naive," said Petrovich.

Chalin is chairman of the local Democratic executive committee and board of elections supervisors. He serves on the state Democratic executive committee. Leander Perez Jr. remains district attorney, despite being indicted for allegedly disbanding a parish grand jury that was about to indict him, court documents show, along with Delta Development Inc., the Perez family oil company, for alleged theft of $72 million in parish oil lease revenues.

Leander says he is innocent and claims he can't get a fair trial in Plaquemines Parish. "It boils down to politics," he said.

State Attorney General William J. Guste is investigating the Perez family company and its oil leases dating back to the 1930s.

The brothers' feud, as locals tell it, began four years ago when Leander wanted the parish to buy him a seaplane. Chalin said no.

Meanwhile, Chalin was backing a new bank to rival the one his brother recently resigned from as board chairman, Delta Bank. The younger brother also struck out on his own in the oil business, say sources close to the family, angering his older brother and two sisters who own equal shares in Delta Development.

"It's Cain and Abel, all over again," Petrovich said of the feud.

When a parish auditor resigned after confessing to embezzling $220,000, Leander launched his own investigation of council affairs. Several commissioners were indicted on minor unrelated charges, including Petrovich and Chalin. The cases were thrown out on appeal.

As commissioner, Chalin Perez negotiated agreements with major oil companies involving land that his family had joint oil interest in with the parish, according to oil company memos. The family ownership of Delta did not surface until Chalin testified at a 1980 commission hearing. He said there was no conflict, claiming the interests were "parallel."

He was "just a little kid shooting marbles" when the family's oil leases were first drawn up, he often says.

About three-fourths of the $42 million annual parish budget comes from oil revenues, at least half of them shared with the Perez family company. Delta earns about $5 million annually from leases on parish land, Petrovich estimated.

It was through such wealth and political manipulation that Judge Perez, who served on the district court bench for six years and kept the title down through the years, held sway over an ethnic mix of 28,000 creoles, blacks and slavic immigrants.

Until now, "the only two years of democracy in my whole life was in the U.S. Marine Corps," said George Pivach Jr., 52, a real estate broker who recalled he was once handcuffed by Perez deputies for protesting a drainage canal across his property. He was released after it was dredged.

Perez once delivered 3,977 votes for Huey Long when the "Kingfish" ran for the U.S. Senate in 1930, even though there were only 2,454 registered voters in the parish. Among those on the rolls: Herbert Hoover, Babe Ruth, Charlie Chaplin. Russell B. Long carried 90 percent of the Plaquemines votes on his first Senate outing, but only 10 percent after he fell out with the judge.

"He wasn't a dictator," said Leander Perez Jr. "Under him, we had a benevolent autocracy."

After Perez was excommunicated by the Catholic church for urging locals to fight integration of local parochial schools, he quipped that he would start his own religion, "the Perez-byterians."

Perez once refurbished a rattlesnake-infested Spanish fort on an island to house civil rights "agitators," should any dare enter Plaquemines Parish. None did.

"It's like July 4, 1776," laughed Curley, the first woman council member, after her historic vote rolled in this weekend. "We've come a long way, baby. The judge is probably turning over in his grave."