United Auto Workers President Owen Bieber today targeted General Motors Corp. for the union's effort to reach a contract settlement and for a nationwide strike if no agreement is reached by midnight Sept. 14.

"I have made a determination that the moment is right to narrow our focus and concentrate on one company," Bieber told reporters at UAW headquarters here.

"GM, in my view, offers the best opportunity for an agreement which will achieve our principal goals: meaningful job security and an economic settlement that represents equality and fairness for our members," he said.

The selection of GM, which employs 350,000 UAW members, means that contract talks temporarily will be suspended at Ford Motor Co., which has 114,000 UAW workers. Chrysler Corp., which is on a separate timetable, has a contract that runs through October 1985.

Strike preparations were under way today at some UAW locals in the Detroit area, but union and GM officials expressed optimism that a walkout could be avoided.

The last time the UAW struck GM was in 1970; the last time the UAW struck an auto maker was in 1976, against Ford.

Industry and union sources said they thought Bieber's choice was motivated partly by the belief that GM, with profits of $3.7 billion last year, could better afford a settlement favorable to the UAW than could Ford, which had a $1.9 billion profit.

The sources said the union also may believe that Ford would be more likely to follow a GM settlement than the other way around.

[Ford's chief negotiator, Peter Pestillo, told the Associated Press that any agreement with General Motors would affect contract talks later at the Ford Motor Co., but "will not necessarily control what we do."]

At separate news conferences, Bieber and GM Vice President Alfred S. Warren Jr. cited progress at the bargaining table.

"We are pleased at the opportunity to lead in this very serious situation," Warren said.

"We think now is the time for development of an agreement that will permit us to be competitive . . . and at the same time satisfy the needs of our employes and our union."

Bieber said he was encouraged by "most fruitful" progress since Aug. 29, when GM and Ford made what he called "totally inadequate" initial contract offers.

Warren, GM's chief of industrial relations, also said there had been progress on health-care issues and contract language.

Neither side will discuss bargaining in detail, but the crucial issue is said to be the union's demand for guaranteed job security in the wake of layoffs of more than 200,000 UAW members during the recession.

"Out-sourcing" -- the increasing use of suppliers at nonunion or foreign facilities -- is a key issue because it eliminates UAW jobs.

Industry sources said GM is a more important target for the union because, although it "out-sources" a lower percentage of its product than Ford, it may be planning to increase the practice.