Relief is coming for Metrorail riders who are fed up with Farecard machines that shine their red "out of service" lights and fare gates that swallow cards. But riders will have to be patient--improvements promised by Metro will take years to complete.

Later this year, the transit agency will begin a program to strip down and rebuild the pulleys, belts and rollers that zip cards through the mechanical innards of the vending and Addfare machines, and to replace similar "transport" systems in the gates with redesigned, more durable ones.

Early in May, Metro will begin testing a new type of dollar-bill scanner as a possible replacement for current ones that so often reject perfectly good money. One vending machine at the Pentagon and one at Silver Spring will have the new devices, which accept bills with either end forward or either side up.

Metro's costly and failure-prone fare-collection system ranks among riders' most serious complaints with the subway. Metro had given serious thought to scrapping it altogether, but now promises the problems can be ironed out.

Metro plans to spend $500,000 on transport components and other parts to place in operating Farecard machines so their aging equipment can go to workshops at Metro, be stripped down and rebuilt and then reinstalled.

Rail operations chief Joe Sheard said technicians will probably start with machines in Red Line stations between Rhode Island Avenue and Dupont Circle, the first segment that opened in 1976. It will take five years to get to all of the rail system's machines.

Transport systems in Metro's 462 fare gates, meanwhile, are to be replaced with a superior design that was tested recently at Farragut West, Sheard said. Installation of the new devices is scheduled to begin this fall, with completion by the summer of 1983.

Metro also plans to equip kiosks with "Farecard validators," electronic boxes that can read where a particular card entered the system, helping attendants to combat fare fraud. In addition, the transit system may test machines that will sell Farecards to credit-card holders, who would receive the bill in the mail later.