An unidentified young man died yesterday when he plunged into the path of a train at the Rosslyn subway station in Arlington, Metro transit police reported.

His death, the third apparent suicide in Metro's 2 1/2 years of operation, disrupted all Blue Line service at the Rosslyn station between 1:35 and 3:05 p.m. Trains passed in both directions through the station on another track without stopping.

Passengers were shuttled by bus to and from Foggy Bottom and Arlington Cemetery, the two adjacent stations on the line. At the peak of the disruption, several hundred would-be passengers milled about as fire and rescue equipment coverged on the station's North Moore Street entrance.

Metro spokesmen said the victim, a white man believed in his 20s, apparently was killed by the impact of the train and was pronounced dead on arrival at Arlington Hospital. An initial check of the clothing produced no identification, one spokesman reported.

Witnesses on the platform reported the man jumped directly into the path of the Washington-bound train as it was slowing for a stop at Rosslyn en route from National Airport. Three of the train's four cars passed over his body before the train halted.

All passengers were instructed by loudspeaker to leave the train and the station.

Arlington police, firefighters and rescue teams were announced to the scene, along with Metro transit police and officials.

Cody Pfanstiehl, the chief Metro spokesman, said the train's cars were uncoupled to provide access to the body. He said the man's body was between the rails, and not mangled by the train's wheels.

The Rosslyn station, deepest on the Metro system, also is one of its busiest, serving more than 12,000 entering passengers each weekday.