In an apparent effort to head off an explosive confrontation with the United Auto Workers, General Motors Corp. yesterday invited the union to organize its new plants in the South and Southwest.

The action ended more than a month of private negotiations between the company and the union over GM's so-called "Southern Strategy" against the unionization of its new plants.

GM President Elliott M. Estes said in a statement issued in Detroit that the company is adopting a "new hiring procedure" that would give preference at its new plants to current union employes.

More importantly, Estes said the company would have no objection to the UAW becoming the bargaining representative at any of its new plants.

The UAW immediately hailed the GM announcement as a major victory. "GM's statement and the procedures agreed upon should make it clear to workers at a nonunion GM facility that they are absolutely free to choose union representation without fear of reprisals," said UAW President Douglas Fraser.

Fraser said the announcement made it clear that GM had abandoned its Southern strategy. "It is particularly significant that Mr. Estes declared explicity that General Motors has no objections to the UAW becoming the bargaining representative of workers in new GM plants," Fraser said in a statement issued by the union in New York where the UAW's International Executive Board is meeting.

Company and union sources said negotiations for the new agreement began Aug. 1 at a face-to-face meeting between Fraser and GM Chairman Thomas A. Murphy to discuss "items of concern."

At that meeting, Fraser warned Murphy that the company's efforts to prevent the unionization of its new plants could result in an explosive situation at the bargaining table. "He told them, "If you want war, you'll get war," a union source said.

Two weeks earlier, culminating a winter of frustration over labor's failure to win congressional approval of the controversial labor law reform bill. Fraser publicly lashed out at the nation's business community for its growing antiunion behavior.

"Where industry once yearned for subserviant unions, it now wants no unions at all," Fraser said at the time. And General Motors was a case in point, he said. Citing the company's Southern strategy, Fraser said, "My message should be very clear: If corporations like General Motors wants confrontation, they cannot expect co-operation in return from Labor."

Fraser repeated his warning to Murphy at the Aug. 1 meeting, according to both union and company sources.

Several days later, Murphy called Fraser with the message: "We'll work it out," sources said. The new hiring policy then was worked out in negotiations between the union and GM's labor relations department.

In its announcement yesterday, GM said the new hiring policy would begin with the opening of the company's new assembly plant in Oklahoma City, Okla. The plant is scheduled to begin operation next spring.

But the new pro-union policy actually went into effect immediately at four new GM plants at Three Rivers and Constantine, Mich., Albany, Ga., and Tuscaloosa, Ala., under provisions of the existing UAW contract.

The remainder of the new GM plants involved in yesterday's announcement either are still on the drawing board or under construction. The new plants, in addition to Oklahoma City, will be located in laurel and Meridian, Miss, Shreveport, La., Fitzgerald, Ga., Athens. Ala., Wichita Falls, Tex., and Fredericksburg, Va.,

Union sources said yesterday that Fraser was "walking on cloud nine" as a result the GM announcement.

In the GM announcement, however, Estes said that, in exchange for the new agreement, the company expected the union to take a "constructive approach" toward increased productivity at the new facilities. There was no further explanation of what specific trade-offs might be involved in the new agreement.

Company sources indicated yesterday that there had been no consultation between GM and other major corporations that opposed the labor law reform bill prior to adoption of the new policy.

One GM source said the company anticipated that one of its immediate problems would come from some of the southern communities that had given GM tax breaks to relocate in their area. Most of these communities had expected GM to keep the union out of the new plants he indicated.