A CSX freight train loaded with coal derailed in Frederick County early yesterday on a Maryland railroad line that is the focus of a federal investigation stemming from two recent derailments near Metro tracks in the Washington area.

The latest incident, which occurred shortly after midnight in the small Potomac River town of Weverton near the West Virginia border, involved 16 cars in the middle of a 152-car train bound from Cumberland, Md., to Baltimore. No injuries were reported, and railway officials said they expected service on the line to resume today.

CSX Corp. spokesman Tim Hensley said that one of eight friction bearings on the 69th car overheated and caught fire, causing an axle to melt and drop onto the track. The train had passed a sensor designed to detect defective equipment 44 miles earlier with no evidence of problems, he said.

"It's a malady as old as railroading, not something you can prevent," Hensley said. "I wouldn't call it a major derailment. A lot of what's involved here is Murphy's Law."

S. Mark Lindsey, chief counsel for the Federal Railroad Administration, said yesterday that he had not been notified of the Weverton derailment. Other federal officials could not be reached for comment.

The incident comes at a time of growing concern among congressional, federal and local officials and proposals for tougher federal oversight of railroads and rapid transit systems after partial derailments of CSX trains running parallel to the Metro system's Red Line in June and this month.

On June 19, 21 cars of a CSX freight train carrying automobiles, food and paper derailed north of the Takoma Metro station in the predawn hours before subway service began. The derailment cut off Metrorail service between Silver Spring and Northeast Washington for three days.

In its investigation, the railroad administration has focused on a bro- ken center beam on a refrigerator car as a possible cause, Lindsey said two weeks ago during a House subcommittee hearing.

On Sept. 5, 12 cars of another CSX freight train jumped the track less than two miles south of the first incident, disrupting Red Line service again. Although Metro was operating, no Metro trains were in the vicinity and no one was injured, although some nearby residents were evacuated.

A worn track switch has been identified as the possible cause of that wreck, Lindsey said.

Yesterday's incident, like the previous two, occurred in CSX's Baltimore division, the subject of a continuing audit by the railroad administration.

The agency recently completed an inspection of the 74 miles of CSX track between Harpers Ferry, W.Va., and Silver Spring, including the Weverton section. Hensley said that no major problems were found. CSX restored the speed limits it had voluntarily lowered during the inspection period.

In all three derailments, the trains were running below CSX's 55-mph limit for freight trains. The train that derailed at Weverton, a so-called extra or unscheduled train, was traveling at 28 mph, Hensley said.

One witness described the derailment site, which is in a rolling rural area three miles east of Harpers Ferry, as a jumble of boxcars crunched in accordion shapes, with coal strewn around the site and a dozen workers beginning a cleanup with bulldozers and cranes.