A man was struck by a train and killed last night in the Rockville area in the fifth railroad fatality in Montgomery County this year.

The incident occurred about 8:40 p.m. east of the crossing at Randolph Road and Nebel Street, according to a spokeswoman for CSX Transportation Inc., which owns the tracks.

Two men were fatally injured in that vicinity in March, and four people were killed by trains there in three incidents in the 1990s. Three of those four deaths were ruled suicides.

A preliminary investigation indicated that last night's incident may have been a suicide, said Lt. Eric Burnett of the county police. He said witnesses told investigators that the man, whom police did not identify, lay down in front of the train before being struck.

The man was struck by an eastbound freight train, which had two locomotives and 65 cars, said Jan Covington, the CSX spokeswoman. It was carrying mixed freight from Saginaw, Mich., to Baltimore, she said.

Speeds of up to 55 miles an hour are permitted where the incident occurred, Covington said. Some trains traveling at that speed may require as much as 11/2 miles to stop, she said.

In the March incident in that area, two men were killed when they were struck by an Amtrak train about one-quarter mile west of the crossing.

In this year's other incidents, a Rockville man was killed in March in Gaithersburg, and a man was killed in February in Kensington.