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.
Gus Buenz, a spokesman for General Motors' attorneys, said that the company was pleased that jurors ''dismissed the vast majority of claims - about 38,000.'' But he said that the company would seek to have the verdict dismissed. 'Victory for Consumers'
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. Division on Cutoff Date
The jurors, who began deliberations Thursday, had reached that part of the decision yesterday but wrote in a note to 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 today, deliberated for almost three hours, then ruled that as many as 36,000 customers who bought their autos after that date would receive no money, Mr. Boyle said.
The April 10, 1977, date was central in the trial. Thomas Gottschalk, an attorney for General Motors, contended that because of widespread publicity generated from the filing of the lawsuit in the spring of 1977, any person buying an Oldsmobile after that date would have been aware of what he was getting. 50,000 Bought Vehicles
The case involved 50,000 purchasers of 1977 Oldsmobile Delta 88's, Omegas and Custom Cruiser station wagons that were equipped with Chevrolet 350-cubic inch engines instead of the highly publicized Oldsmobile ''Rocket'' 350-cubic inch engines.
William A. Harte and Mr. Boyle, representing the customers, argued that General Motors had breached written and implied warranties by selling the ''Chevymobiles'' and asked the jury to award as much as $131 million to the purchasers.
General Motors contended that it had informed its dealers of the engine switch as early as September 1976 and maintained that the Chevrolet engine was just as good as the ''Rocket'' engine it replaced.
Mr. Gottschalk, the auto maker's attorney, also argued that the practice of changing engine parts had gone on at General Motors for ''many years.'' He said that the name on the auto meant that the division stood behind the product, not that it had made all the parts.
The damages sought included two cents a mile for alleged inferior durability, design and drivability of the Chevrolet engines.
