A Federal jury ruled today that the General Motors Corporation must pay $550 to each of more than 10,000 purchasers of 1977 Oldsmobiles that contained Chevrolet engines.
But in a split verdict the jury held that the automobile 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, an attorney for the plaintiffs in the 10-week trial that sought $131 million in damages from General Motors, the nation's largest auto maker.
State Attorney General Tyrone Fahner, whose predecessor, William Scott, first 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.''
''This case shows that companies which do business in this state must deliver what they promise,'' he said. ''The jury clearly says that advertising is a type of warranty.''
The six jurors said that people who bought Oldsmobiles with Chevrolet engines before April 10, 1977, were entitled to refunds of $550 each.
Mr. Buenz put the number of claims to be paid at 10,688, but Mr. Boyle said the number could go as high as 17,000. Taking a figure of 15,550, as an example, General Motors would owe $8.2 million.