Harold Brazil, a former utility company official taking his first leap into District politics, ousted four-term D.C. Council member Nadine P. Winter from her Ward 6 seat yesterday.

In a narrow upset that was one of several pivotal changes apparent in the council's makeup, Brazil tallied 43 percent of the vote, and Winter had 39 percent. Winter, a member of the council for 16 years, ran with more money than Brazil and had the backing of influential ministers, but she apparently fell victim to residents' yearning for change.

Meanwhile, in other council races, John A. Wilson scored an overwhelming victory in the Democratic race for D.C. Council chairman, and school board member Linda Cropp gained the Democratic nomination for an at-large seat.

Two other incumbents, Frank Smith Jr. in Ward 1 and Harry Thomas Sr. in Ward 5, won the Democratic nominations for new four-year terms.

Wilson's likely elevation to council chairman, and Brazil's upset of Winter, set the stage for significant change to the 13-member council, which is also losing some other veteran members. Wilson is poised to replace Chairman David A. Clarke, who chose to run for mayor instead of seeking reelection. And Betty Ann Kane, a council member since 1979 who ran for D.C. delegate, also is leaving.

Those departures were expected, but Brazil's bid to topple Winter was considered a long shot by many political observers. Brazil, 43, is a former lobbyist for Potomac Electric Power Co. and a former prosecutor with the U.S. Attorney's Office. He credited his victory to the door-to-door campaign he waged across the ward.

"I think voters are ready for a change," Brazil said last night. "The government has not been working well, and she is part of that problem."

Brazil had support from business and neighborhood groups in Ward 6, which spans parts of Northeast and Southeast Washington, including Capitol Hill, Lincoln Park and Anacostia. He also apparently benefited from a surge of new Democrats in the ward. Bob Boyd, the Ward 6 school board member, who supported Brazil, said 9,000 residents had become Democrats since 1987.

"There was a fairly strong anti-incumbent mood among new voters," Boyd said.

Winter, who conceded to Brazil by telephone late last night, had been endorsed by several influential ministers, including the Rev. Willie Wilson, pastor of Union Temple Baptist Church in Anacostia; Bishop Smallwood E. Williams, pastor of Bible Way Temple; and District African Methodist Episcopal Bishop H. Hartford Brookins.

But she was criticized for failing to block a major increase in parking fines and for helping lead the effort to scale back Initiative 17, the city law that provides emergency shelter to anyone requesting it. She also suffered from complaints that she had lost touch with constituents' concerns.

"I think Nadine is tainted because she's been in there too long," Ward 6 resident Robert Stevens, who voted for Brazil, said yesterday.

In the council chairman race, Wilson, who, like Winter, had been on the council since it was formed, had 82 percent of the vote. His only rival in the race, Vincent Orange, a lawyer waging his first D.C. campaign, had 18 percent.

In the at-large race, Cropp finished with 51 percent of the Democratic vote, former congressional aide Johnny Barnes had 27 percent, and housing activist Terry Lynch had 22 percent.

In Ward 1, Smith had 62 percent of the Democratic vote, and Richard M. Landis, a local lawyer, challenging him for the second time, had 38 percent.

In Ward 5, Thomas won with 49 percent of the vote. His nearest rival, community activist Robert Artisst, had 30 percent of the vote.

Ward 3 council member Jim Nathanson, who also is seeking a second term, was unopposed in the Democratic primary. He will compete against community activist Julie Finley, the Republican candidate, in November.

Although Wilson and the winners in the ward races for council are expected to go on to victory Nov. 6 because they have no formidable opposition, the at-large race is hardly settled.

Mayor Marion Barry, who was convicted last month on a single count of cocaine possession, quit the Democratic Party, registered as an independent and announced he would seek an at-large seat on the council. He is set to challenge Cropp, as well as at-large council member Hilda H.M. Mason, who ran unopposed in the Statehood Party primary, and several other independent candidates. The top two vote getters gain council seats.

This fall, council members will be forced to confront the city's fiscal problems and may have no choice but to raise taxes or make drastic spending cuts. Wilson, a strong critic of how Barry has handled the D.C. budget, has vowed to wield great influence over city finances.

He has said he wants to expand the council's power and prestige by giving it more oversight of the city's public school system (a half-billion-dollar operation), allowing it to alter zoning commission decisions and increasing its authority over city taxes and bonds.

But Wilson will face many other tests, among them bringing order and cooperation to a legislative group that at times has been paralyzed by bickering or mired in battles over money with Barry.

"We're going to be faced with the most difficult period in the city's history during the next four years," Wilson said last night. "We have major financial problems. It's going to be a tremendous amount of work."