General Motors Corp. yesterday agreed to a United Auto Workers demand that any wage and benefit concessions it wins from the union be reflected in the sticker price of its cars and trucks.

"General Motors welcomes the UAW's historic proposal to reduce significantly our present labor costs in return for a reduction in prices," GM Chairman Roger B. Smith said yesterday in Detroit, where the UAW's GM and Ford Motor Co. bargaining committees are involved in emergency contract negotiations.

"We are prepared to respond to significant reductions in labor costs with equally significant reductions--beginning immediately--in the consumer prices of all new GM cars and trucks sold in the United States," Smith said.

Contracts between the UAW and the nation's major auto makers do not expire until Sept. 14. But the union, faced with massive layoffs and continued slumping sales in the industry, agreed last week to early contract talks in an effort to help save millions of dollars for the two companies.

Monday, the union set a Jan. 23 deadline for reaching agreement on a concessions package in which any givebacks to the industry would be tied to some form of job security.

The union's proposal was torn from the pages of the UAW's early history. In 1945, the UAW demanded that GM open its books so that the union could determine how much the company could afford to pay its workers without having to raise the price of its cars and trucks. Now, some 37 years later, in the midst of what many are calling a depression for the domestic auto industry, GM appears ready to tie reductions in labor costs to reductions in consumer prices.

UAW President Douglas A. Fraser, who for months has been saying that 1982 would be marked by "creative bargaining," said yesterday: "There will be no economic concessions to General Motors. If we reach an agreement which our members at GM believe addresses their problems, any concessions will go to the consumer, not to the corporation."

Fraser said the proposal was offered both in the spirit of altruism and practicality.

"When GM executives look across the bargaining table, we want them to see advocates on behalf of GM workers and also the consumers who buy the products we build . . . . The price reduction must be large enough to be meaningful and in place for an extended duration," Fraser said.

Practically speaking, "Lower prices for car buyers should stimulate the total car, truck and van sales in the United States and benefit the entire domestic auto industry," Fraser said.

That industry has lost nearly $5 billion since 1980. It currently has about 214,000 workers on indefinite layoff and close to 70,000 more workers are on what is described as short-term furlough. Domestic car sales in 1981 dropped 5.3 percent below their 1980 level, down to their lowest mark in two decades.

When all of the 1981 figures are in, GM is expected to report a $300 million profit. Industry forecasters are predicting that Ford will have lost $1 billion during the same period.

Fraser said yesterday that GM agreed to the consumer proposal "as part of a broader framework on which current collective bargaining will be based." That framework, from the union's viewpoint, includes:

* Independent certification by a public accounting firm, agreed upon by both parties, "to examine the necessary financial data so that the consumers and the workers can be completely confident that all cost savings are passed through to consumers."

* Job security proposals, particularly protection against the exportation of UAW jobs to overseas subsidiaries.

* "Equality of sacrifice" by nonunion GM employes, including top management.

* An automatic return to economic provisions in the current GM contract--a point that seems to indicate that the union will, indeed, sacrifice monetary and other benefits in the current round of bargaining.

* An open-ended contract with no expiration date.

In agreeing to the union's demands, GM's Smith said, "Our objective is to save jobs, not only in General Motors, but also in our supplier industries."

On the matter of opening the company's books, he said: "General Motors is prepared to agree to a means that would independently verify that the entire reduction in labor costs would be passed along to the consumer."

UAW officials said last night that an identical union demand had been made in the Ford talks. Ford had not yet responded.