Metro officials have told train operators to manually run the subway's newest rail cars after an incident Tuesday in which doors remained open as a train was moving -- a serious malfunction of the automatic system that is supposed to ensure that doors are closed before a train can move.

No one fell from the open doors of Car 5190 or was injured as the Orange Line train started rolling from Metro Center toward New Carrollton about 3:20 p.m., said Steven A. Feil, Metro's chief operating officer for rail. A passenger on the train hit the intercom button and told the operator that the doors were open, he said. The train had moved about 10 feet before the operator deployed the brakes and the train was taken out of service, Feil said.

Later that day, Feil ordered train operators to use manual controls when running any of the 192 rail cars manufactured by Spain-based CAF Inc. That means the train operator is responsible for opening and closing the doors instead of relying on the onboard computers that normally perform that function.

"I don't know what happened, but I can caution on the side of safety until we figure this out," Feil said, adding that Metro officials are seeking witnesses as they investigate the incident. "We want to make absolutely certain that we can either duplicate this or come away with a certainty that it can't happen."

The door malfunction is the latest in a string of problems surrounding Metro's $383 million purchase of the CAF cars. The troubles include poor reliability, shoddy workmanship and concern that a design flaw might have caused four CAF cars to derail in an 18-month period ending last fall.

Metro officials are studying whether the design of the rail cars makes them prone to jumping the tracks. In each case, the trains derailed in places where the track was worn. None was carrying passengers, and all were operating at a low speed while rounding a sharp bend, typically found in rail yards and not on the main railroad. For those reasons, Metro officials decided against pulling the cars from service.

The CAF cars, the last of which were delivered in 2004, are equipped with sophisticated computer software, including the equivalent of an airliner's "black box" to give mechanics precise information about malfunctions. Software bugs on the highly automated cars have bedeviled Metro engineers; once they fixed one, others would spring up.

Metro records point to basic manufacturing defects: faulty wiring, sloppy assembly and substandard materials that the agency had approved. Many of the defects were not discovered until after the cars were built, because Metro and CAF failed to perform sufficient checks along the assembly line to monitor the manufacturing process, according to records and to interviews with Metro officials.

As the cars went into service, defects were evident, according to Metro records. Some cars would not accelerate; others had faulty air conditioning. In some cases, doors did not close. In 2001, with 78 cars built, Metro took the unusual step of halting production for three weeks. It told CAF to improve quality and redesign its assembly line. Production resumed, but troubles with the cars continued.

In January 2002, a 58-year-old woman's arm became caught in a door, and she was dragged along the platform at Gallery Place because of a faulty circuit in a CAF car. Two months later, a fire erupted on another CAF car. Metro traced the problem to an incorrectly wired heater. The problem was found on 33 other CAF cars, even though CAF and Metro employees had inspected and approved the wiring of the heaters, according to an internal investigation.