The Supreme Court yesterday removed a potential barrier to an antitrust class action in behalf of 300,000 Mercedes-Benz owners who had repairs done by franchaised dealers in a four-year period after the warranties on the cars had expired.

The lawsuit was filed in March, 1974, by two Philadelphia-area owners in behalf of themselves and all other owners and lessees who had nonwarranty repairs performed at any of 588 dealerships since March, 1970.

They alleged that the defendants, Daimler-Benz, A.G., of West Germany, and Mercedes-Benz of North America, Inc., which Daimler owns, had conspired with the dealers to fix the prices of parts and labor for nonwarranty repairs, and to fix the prices at artifically high levels.

The suit also asked for a jury trial.

Daimler moved unsuccessfully for dismissal of the case. Then a federal judge, in a tentavtive order, certified the suit as a class action.

He also held out the possibility of trial by one jury to determine liability, a trial by a second jury to determine damages if the defendants are first ruled liable, and, before the start of the second trial, a re-examination of the calss certification.

Daimler, contending that a class action involving 300,000 potential claimants and between 4.0 million and 12 million customer-repair invoices is unmanageable, appealed to the Third U.S. Circuit Court of Appeals.

The appellate court ruled that the question of manageability was for the trial judge to decide. Yesterday, the Supreme Court refused to review the ruling, thus clearing the way for the resumption of preliminary legal skirmishing.