Metro's now-famous driverless train of last Monday appears to have a previously unreported predecessor.

Last April 2, passengers in the front car of a Blue Line Metro train milled around inside the operator's cab and admired all the gadgets as the train sped toward the Foggy Bottom station without the visible help of an operator, one of those passengers said yesterday.

The April incident was reported at yesterday's Metro Board meeting by board member Francis B. Francois after Metro General Manager Richard S. bPage reported on the incident Monday on the Red Line.

"That's not the first time this has happened," Francois said. He referred reporters to Robert Stahl, a U.S. Patent Office employe who told of the April 2 incident.

In an interview yesterday Stahl saidthat the operator was having trouble getting his Virginia-bound train to go on the Blue Line. The operator left the cab and shortly thereafter the train took off. It went through two or three stations, Stahl said, while passengers wandered into the cab and looked around. Nobody panicked and the doors never opened.

"We went to another station, the train stopped, and the same identical operator opened the door from the outside," Stahl said. "He asked the people to leave his cab, and the train continued without further incident." t

Stahl said he called Metro that day and complained about the incident and that he was called back a week later by Metro officals who "would neither confirm nor deny that it happened." Stahl could not remember the name of the person he talked with.

Metro officials, badly embarrassed by Monday's highly publicized incident in which a woman jimmied open the door of a cab and stopped a driverless train, said yesterday they could find no record of the earlier incident. But they said they will investigate both.

Officials theorized that in the incident Stahl described, the train operator had chosen to operate the train from a cab in a center car -- a technfique used somethimes to overcome trouble. However, special flagging procedures are required in that case, and no one is supposed to leave the cab door open.

Officials said there was no danager to riders, because the master Metro computer controls speed, braking and following distance regardless of whether an operator is present.

In other action yesterday, the board directed Page to develop specific proposals for simplifying Metro's Byzantine fare schedule and possibly eliminating or making more reliable the Farecard farecollecting system.