Top officials of the beleaguered United Auto Workers, the nation's third-largest labor union, yesterday chose Owen Bieber, vice president in charge of its General Motors department, to succeed retiring president Douglas Fraser.

Bieber, 52, is expected to be officially ratified at the UAW convention in Dallas next May.

Fraser's retirement, mandatory because he is 65, is widely viewed as the end of an era. He is the last UAW chief to be drawn from the inner circle of the late Walter P. Reuther, the leader during the Depression who forged the union into a potent social and political force. He also is the last who has combat ribbons from the violent labor battles of that period.

"The difference is that Reuther, Woodcock, Fraser -- those men shaped the union," a UAW spokesman commented. "Owen was shaped by the union."

Bieber will inherit a union that is no longer the humming, big-finned juggernaut of organized labor, but a humbled one that is more like a flivver on a road full of pot- holes.

As the auto industry reeled from soaring fuel prices and foreign competition, the union's membership plummeted from 1.5 million in the late 1970s to just over 1.1 million. Used to being an elite among American industrial workers, they endured a series of "give-back" agreements with auto makers that left them for the first time with less, not more.

"We have represented the membership well in the past and will represent it well in the days ahead," Bieber told reporters after his nomination was announced.

His selection is unlikely to lead to any significant change in philosophy at the union, he added.

Bieber's colleagues do not describe him in the same flashy terms as they do the man whose shoes he will fill. He is, they say, "steady," "solid, hardworking, deliberate, a nuts-and-bolts bargainer, warm and compassionate."

Bieber emphasized that Fraser would continue to be firmly in charge until May. Meanwhile, he said, he will be campaigning among the rank and file, even though the ratification of the nominee by the delegates at the convention traditionally has been a rubber-stamp process.

"A lot of things have happened in the union lately that have never happened before," said one union source.

Raymond Majerus, 58, the union's secretary-treasurer, was regarded as Bieber's chief competition for the post. But after the announcement of Bieber's selection he said he is "totally and completely in support of Owen Bieber."

Donald Ephlin, 57, head of the UAW's Ford Division and another front-runner, said, "This is more like a team picking a captain. We're all on the team. We'll go forward."

One of Fraser's deepest concerns as he approached the selection of his replacement has been the possibility that, under the new chief, the union might abandon its tradition as a progressive social force, he said in a recent interview. This possibly was a role that UAW leaders could afford to play only as long as times were good.

All of the candidates for the top job had expressed a commitment to what they call the "Reuther legacy" of an activist compassion for the poor.

As head of the union's GM department, Bieber holds the office that has propelled two others into the union leadership. Reuther, who died in a 1970 plane crash, and Leonard Woodcock, now a professor at the University of Michigan, each headed the GM department.

Known as a friendly, down-to-earth man, Bieber was said to have the best relationship with the union's regional directors, who are a majority on the 26-member executive board, which made the selection. He also recently won the endorsement of a dark-horse candidate who dropped out, vice president Steven Yokich.

Bieber drew both praise and criticism earlier this year for his handling of the rocky GM contract negotiations, which produced an agreement that was almost rejected by the rank and file as too concessionary. Initially the favorite for the presidency, his star had waned during this period.