The United Auto Workers, reviving a long-standing proposal that never has been accepted by the auto industry, offered yesterday to moderate its wage demands if the General Motors Corp. agrees to freeze prices for the life of its new contract with the UAW.

The union also would "take another look at our demands" if GM can "prove that our demands are inflationary based on our productivity," UAW President Douglas A. Fraser said on ABC-TV's "Issues and Answers" program yesterday.

Last week the UAW chose GM, the nationa's biggest corporation and the strongest of the Big Three automakers, as its strike target for negotiating a new three-year contract with the auto industry. Yesterday, confirming earlier indications from bargaining sources, Fraser said that both the negotiating atmosphere and chances of avoiding a strike are "good".

GM had no immediate comment on Fraser's proposals, but chances are considered almost nil that the company would agree to a price freeze -- or to Fraser's suggestion that it roll back its 3.1 percent price increase announced last Friday. A rollback "would be very healthy for the economy . . . and give the rest of the people in the United States the hope that everybody would moderate their demands," Fraser said.

Asked if the UAW also would do so, Fraser said: "We would moderate our demands if we could get a commitment from General Motors that they would not increase their prices during the life of our agreement . . . That historically has been our position."

A UAW spokesman said such an offer was first made by the late Walter Reuther during negotiations right after World War II and repeated periodically thereafter, although it has not figures in the last couple of bargaining rounds.

Fraser, who earlier told the Carter administration to "stay the hell out" of the auto talks, indicated it has done so. Although the auto negotiations covering more than 700,000 workers are considered the year's most important, Fraser said he'd been told anti-inflation officials would be getting in touch with him. None has done so yet, and "It's a little late in the game," he said.

On politics, Fraser and another union president, William H. Winpisinger of the International Association of Machinists, disagreed with Labor Secretary Ray Marshall over the labor movement's support for President Carter's reelection.

Appearing on CBS-TV's "Face the Nation," Marshall said Carter has "one of the best labor records of any president in recent memory" and will have "overwhelming labor support if he runs again.

But Fraser said Sen. Edward M. Kennedy (D-Mass.) is viewed as more desirable and electable than Carter among local UAW leaders. On NBC-TV's "Meet the Press," Winpisinger, who is heading a draft-Kennedy drive, said: "There is nothing he (Carter) can do to redeem himself with the machinists' union. He has gone to the well too many times . . . and come up dry."

Fraser said his support for Carter will hinge on who runs against him, while Winpisinger called himself an "ABC guy . . . anybody but Carter." But, like Fraser, Winpisinger said he couldn't support any of the most predominantly mentioned Republicans.

Meanwhile, on the eve of the nation's Labor Day observance, President Carter issued a statement describing inflation as the most serious problem facing workers.