Thirteen persons were injured, one man critically, when a Montgomery County Ride-On bus en route to the Grosvenor Metrorail station crashed into a tree in the 5000 block of Strathmore Avenue in Kensington yesterday afternoon, Montgomery County police said.

The man, a passenger, remained in critical condition at Suburban Hospital, and the bus driver was in stable condition there last night, a nursing supervisor said. A Holy Cross nursing supervisor said eight passengers were treated there and released, while two were admitted for observation. The identities of those hospitalized were not available last night.

Police are still investigating the cause of the accident, which occurred around 3:20 p.m., a police spokeswoman said. Witnesses said the bus, driven by 31-year-old Michael Anthony Thompson of 1707 Bay St. SE, was traveling west on Strathmore when it began drifting across the double yellow line.

The bus then rolled up an embankment on the far side of the street and struck a tree, pinning Thompson in his seat, a fire department spokesman said.

The police spokeswoman said Thompson received two traffic citations after the accident, one for failure to stay to the right of a double yellow line and the other for failure to reduce speed to avoid a collision.