Washington state's automobile-lemon law, designed to protect consumers who purchase defective new motor vehicles, was upheld today by a unanimous state Supreme Court. The law had been challenged by the Ford Motor Co., which contended it violates the equal protection and due process provisions of the state and U.S. constitutions. ``The state's interest in protecting consumers in the purchase of motor vehicles under the motor vehicles warranties law outweighs the due process considerations,'' Justice Charles Smith wrote for the court. The case stemmed from Ford's appeal to the King County Superior Court of a New Motor Vehicle Arbitration Board ruling in favor of Gary Barrett. Barrett bought a Ford Thunderbird from Mossy Ford in Bellevue in September 1985. He went to the arbitration board after the dealer was unable to repair a steering problem that caused the vehicle to pull to the left. The board ordered Ford to buy the vehicle back from Barrett. Ford conceded that the steering defect constituted a serious safety defect. But the automaker appealed, asking that Barrett's claim be denied on merits and contending the requirement that it repurchase the vehicle was unconstitutional. Superior Court Judge Patricia Aitken disagreed. She ordered Ford to pay Barrett $7,125, representing the repurchase cost less offset for use; $7,000 for Ford's failure to provide free use of a comparable loaner vehicle pending resolution of the appeal; and $1,750 for attorney's fees. In its appeal of tht decision to the state's high court, Ford contended that requiring it to pay attorney fees and a loaner-vehicle fee constituted the singling out of ``a class of litigants and subjecting them to onerous penalties as a condition of seeking redress within the court system.'' Ford also complained that if had prevailed in its superior court appeal, Barrett could not have been forced to pay attorney fees. The company said that represented denial of equal protection under the law for Ford and discouraged the filing of appeals. Smith noted, however, that the law designates two classes, manufacturers and consumers, and that the consumer class is not held liable for fees incurred in an appeal. Smith held that the separation of classes was rational. And he brushed aside Ford's argument that the law might discourage all appeals by manufacturers. He said Ford had not effectively demonstrated that the law was not rationally related to its purpose. ``Equal protection does not require that legislative efforts be perfect,'' Smith wrote, adding: ``The state's interest in (consumer protection) outweighs any deterrent effect on manufacturers.''