A federal jury ruled yesterday that General Motors Corp. must pay $550 each to more than 10,000 purchasers of 1977 Oldsmobiles that contained Chevrolet engines.

But in a split verdict, the jury also said the No. 1 auto maker did not owe damages to at least 30,000 customers who bought "Chevymobiles" after April 10, 1977.

"We possibly will appeal," said Charles A. Boyle, a lawyer for the plaintiffs in the 10-week trial that sought $131 million in damages from GM.

Gus Buenz, a spokesman for GM's attorneys, said the company was pleased the jurors "dismissed the vast majority of claims -- about 38,000." But he said GM would seek to have the verdict dismissed.

State Attorney General Tyrone Fahner, whose predecessor filed the class-action suit, said that while he disagreed with the verdict, it was "a significant legal victory for the consumers of Illinois and the nation. The jury clearly says that advertising is a type of warranty. It is good for consumers, good business and the law to give purchasers what they expect from advertising."

The six jurors said people who bought Oldsmobiles with Chevy engines before April 10, 1977, were entitled to refunds of $550 each.

Buenz put the number of claims to be paid at 10,688, but Boyle said the number could go as high as 17,000.

Taking a figure of 15,550, for example, GM would owe $8.2 million.

The jurors, who began deliberations Thursday, had reached that part of the decision Friday but wrote in a note to U.S. District Court Judge Frank McGarr that they were divided on the case of at least 30,000 others who purchased their cars after April 10, 1977.

They returned to court yesterday, deliberated for almost three hours, then ruled that as many as 36,000 customers who bought cars after that date would receive no money, Boyle said.