A Metro train derailed yesterday afternoon when its two front wheels popped off the tracks during a routine turnaround at the Silver Spring Station, creating delays along the Red Line, the system's most heavily traveled route.

No passengers were on the train when it derailed, and the train operator, who has served in that job for 15 years, was not injured, Metro officials said. But the derailment reduced rush-hour service and slowed evening traffic on the Red Line, conditions that could continue into this morning's commute, Metro officials said.

Outbound Red Line trains terminate at Silver Spring or at Glenmont, the end of the line in eastern Montgomery County. They turn around and head back toward the District and then on to either Grosvenor-Strathmore or Shady Grove, in the western part of Montgomery.

The six-car train that was attempting to turn around yesterday derailed four to six feet from the main line, stopping immediately, officials said.

Because the turnaround area at the Silver Spring Station was blocked by the disabled train, the trains that normally terminate there instead turned around farther south, at the Brookland-CUA Station. That cut in half the train service normally available to Fort Totten, Takoma and Silver Spring. Trains bound for Glenmont made their normal stops, though they slowed through Silver Spring, Metro officials said.

Steven Feil, Metro's chief operating officer for rail, said he was not immediately able to determine what caused the wheels to come off the track. He said that he didn't notice anything unusual during a site survey yesterday afternoon and that the operator was given a standard drug and alcohol test.

Metro said heavy-duty equipment would be brought in at midnight, after the system closed for the day, to lift the train and assess damage to the track.

The incident was the latest in a growing list of problems for the beleaguered 28-year-old Metro system. The Red Line has been particularly hard hit. In recent months, a packed Red Line train was abandoned during rush hour by an operator whose shift had ended; a train operator and two passengers were stranded for at least a half-hour outside the Forest Glen Station when communications systems were knocked out during a storm; and the Red Line was slowed for nine days because of flooding at the Silver Spring Station.

Metro officials said yesterday's derailment was the first of the year and the third in the past two years.

"We feel very fortunate nobody was injured," Metro spokesman Lisa Farbstein said of yesterday's incident. "Our first concern was safety for customers and employees, and in this case, everyone was fine."