John A. Wilson was elected yesterday to lead an increasingly independent D.C. Council as it enters a new era without Mayor Marion Barry, whose bid for a council seat failed.

Democrat Linda Cropp, a school board member, won one of two at-large seats with 38 percent of the vote. Incumbent Statehood candidate Hilda H.M. Mason received 29 percent to claim the second.

Barry was third with 20 percent, apparently hurt by a wave of voters who backed Cropp and Mason to prevent him from resuming his political career.

The mayor's entry in the race once was seen as a fatal blow to Mason's candidacy. But ironically, the vote suggested that he boosted her campaign.

"This is a guilty verdict for which there is no appeal," Mason campaign manager David Splitt said last night of Barry's defeat.

Wilson (D-Ward 2) coasted to victory in the race for council chairman, succeeding Democrat David A. Clarke, who ran an unsuccessful campaign for mayor.

Three other Democratic incumbents -- Frank Smith Jr. (Ward 1), Jim Nathanson (Ward 3) and Harry L. Thomas Sr. (Ward 5) -- posted victories in their races for ward seats.

And in Ward 6, political newcomer Harold Brazil, a lawyer and former Potomac Electric Power Co. executive, trounced Republican rival R. Bradford McMahon.

The race for the two at-large seats was among the hardest fought in the city -- and, with eight candidates in the running, the most difficult to predict.

But Cropp and Mason outran the mayor in every part of the District except Ward 8, which includes neighborhoods east of the Anacostia River and is home to the city's poorest residents.

There, Barry led with 52 percent of the vote, according to partial results. Yet in Ward 3, which includes the largely white and affluent neighborhoods west of Rock Creek Park, Barry ran next to last. Cropp beat Barry in his own precinct, and the mayor was barely ahead of Mason there for the second seat.

As Mason began her victory speech last night, Barry appeared on a television set in the room, prompting jeers from her supporters. She asked them if they wanted to turn the set off. "We've already shut him off," shouted one supporter.

Barry, who quit the Democratic Party in August after he was convicted on a drug possession charge, began his campaign as an independent slowly but in recent weeks had pursued voters day and night.

The mayor raised about $100,000, more than any other candidate, but he received few prominent endorsements. His campaign concentrated on rekindling support among two of his most loyal constituencies: the elderly and working-class blacks who live east of the Anacostia River.

Cropp, who easily captured the Democratic nomination in September, was heavily favored to win one of the two seats. And Mason, 74, was endorsed recently by a majority of D.C. Council members and Jesse L. Jackson.

Yesterday's vote signals a sea change for the council, which functions as the city's legislature.

Along with the departure of Clarke, who served as chairman for the past seven years, the council will lose two other senior members, Betty Ann Kane (D-At Large) and Nadine P. Winter (D-Ward 6).

Kane, who was first elected in 1979, gave up her seat to run for D.C. delegate, but lost to Eleanor Holmes Norton in the Democratic primary. Winter, meanwhile, was defeated by Brazil in the primary. Winter and Clarke were members of the first elected D.C. Council, which took office in 1975.

Their exits will shuffle the leadership of several key council committees. But the biggest change is clearly the rise of Wilson, 46, an outspoken critic of Barry's administration who has warned for some time that the District is nearing the brink of financial collapse.

Wilson, who has represented Ward 2 for 16 years, has vowed to expand the council's power and prestige, but it won't be easy to bring consensus to the group. He also will face problems in dealing with the city's mounting deficit.

Wilson has said he wants the council to have more oversight of the city's public schools, more authority over taxes and bonds, and the ability to alter zoning commission decisions.

"I intend to establish the council as an equal branch of government," Wilson said last night.