Nadine P. Winter's 16-year tenure on the D.C. Council came to an abrupt halt Tuesday at the hands of a first-time candidate who had a secret: hundreds of new Ward 6 voters who Winter apparently didn't know existed.

Harold Brazil, a former utility company official, collected overwhelming support in several Capitol Hill precincts in which twice as many residents voted than in the Democratic primary four years ago, when Winter last ran for reelection.

Brazil credited his victory to intensive door-to-door campaigning in those precincts, where he said he found large numbers of young professionals who were either new to the area or had not voted in the past.

"Harold turned out a vote we had not identified," David Watson, a Winter aide, said yesterday. "He was more aggressive, and it's easier to win an election when you're hungry. We weren't hungry enough." Watson said Winter was "vacationing" and could not be reached for comment yesterday.

Winter's defeat was yet another ingredient for upheaval on the council, which is losing three of its senior members, will have a new chairman and possibly two new at-large members. There also may be a shuffle in the leadership of some of the council's most powerful committees.

"This is the most significant shift in the council I think we've ever had at one time," said council member William Lightfoot (I-At Large), who was elected in 1988.

Although the next council is already taking shape, two citywide seats will remain in doubt until the Nov. 6 general election. School board member Linda W. Cropp (Ward 4), who handily won the Democratic nomination for an at-large seat Tuesday, now must face council candidate Marion Barry, incumbent Hilda H.M. Mason of the D.C. Statehood party, and several hard-charging independents.

Barry, who was convicted last month on one count of cocaine possession, has quit the Democratic party and will compete as an independent, but there is debate among many political analysts as to how he will fare. The top two vote-getters in the race will be elected.

Cropp ran with endorsements from key business, education and labor groups in the primary, and said yesterday she expects to retain that support in the general election. But unlike in the primary, Cropp won't be running with the support of John Ray's well-financed mayoral campaign.

"The ties to Ray helped her enormously," said Lawrence Guyot, a longtime community organizer in the District. "Now she's on her own."

Some activists say Mason, a 74-year-old incumbent with a long civic history here, could be vulnerable to an aggressive campaign by Barry. Mason already has $72,000 to fend him off, but most of it is her own money.

Adding to the air of change in the council chambers will be the departure of David A. Clarke, who was defeated Tuesday in his primary campaign for mayor, and Betty Ann Kane, who lost her bid for D.C delegate. Clarke joined the council in 1974 and has been chairman for seven years; at-large council member Kane was elected in 1979.

Two other veteran council members who lost the Democratic primary for mayor -- Charlene Drew Jarvis and Ray -- will retain their seats.

Perhaps the council's biggest change will be the rise of Wilson, a 16-year veteran from Ward 2, to chairman. Wilson trounced his only Democratic rival in the primary and has no opposition in November. He has vowed to expand the council's power over the city's finances, but will be hard-pressed to bring consensus to a 13-member group often hampered by bickering.

Meanwhile yesterday, newcomer Brazil savored his 43 to 39 percent victory over Winter.

Brazil, 43, once worked as a lobbyist for Potomac Electric Power Co. and was a prosecutor for the U.S. Attorney's Office. His bid to oust Winter was considered a longshot by many political observers, but his support among voters on Capitol Hill -- where he received three times as many votes as Winter -- gave him the victory.

"We ran because we had a mission, and we're getting closer to it," Brazil said. "We found a lot of people new to the area when we went door to door, and there was strong sentiment that the government needed change."