Federal investigators, in a special probe sparked by the derailment of a CSX train in June that severed Metro's Red Line for three days, have discovered an unusually high accident rate and a series of derailments at CSX caused by track and equipment maintenance problems, they said yesterday.

A similar accident Saturday night, in which 21 freight cars wrecked and again cut the parallel Red Line, was the eighth derailment this year in the CSX Baltimore Division, which runs trains through Maryland, the District of Columbia, Pennsylvania and part of West Virginia.

Metro expects to restore full Red Line service in time for the rush hour this afternoon but will continue its shuttle bus service between the Fort Totten, Takoma and Silver Spring stations for the morning rush hour.

The safety performance of the Baltimore division "is lagging behind that of other railroads, and of the CSX system as a whole," said John H. Riley, chief of the Federal Railroad Administration. "We want to find out why." He announced that the agency began an extensive audit yesterday of the Baltimore Division's maintenance and operations.

Through June 1 of this year -- before the two recent accidents -- the division had 6.95 accidents per million train miles, according to federal records. The national railroad accident rate is 4.24.

CSX officials "don't dispute that there has been an unusual incidence of derailments in the Baltimore division," said corporate spokesman R. Lindsay Leckie. "We welcome the audit."

CSX is a Richmond-based railroad holding company that also has operations in energy, telecommunications, information systems and real estate.

The CSX rail network, completed in 1985, includes most of the old Chesapeake & Ohio, Baltimore & Ohio (the predecessor of the Baltimore division), the Western Maryland and the Seaboard Coast lines.

After suffering a $118 million loss in 1985, the company slashed its work force and reduced its operations, cutting its mileage by 9 percent. It turned a profit of $418 million last year and continues to tighten its belt. Total employment will be cut to 30,000 from 42,000 during the next 18 months, one CSX official said.

The number of maintenance workers has dropped 13 percent in the past two years as many jobs have been automated; at the same time, the number of freight cars has been reduced by 24 percent and the number of locomotives by 18 percent, a spokesman said.

"There is absolutely no correlation between the work force reductions and derailments," said CSX's Leckie. He said the company has not reduced its maintenance standards, and has "not found any common thread that would tie any of these derailments or their causes together."

But the FRA's Riley said, "There has been an unusual number {of derailments} caused by equipment or track maintenance problems . . . . We've seen enough to make us concerned."

The federal investigation of the Baltimore division's operations will "assess every phase of the . . . operations, from hardware issues like track and signal inspections, to training, communications and accountability issues," Riley said.

CSX has said that the June 19 derailment, in which 21 cars derailed just north of Metro's Takoma station, was caused by a broken center beam on a refrigerator car. There has been no official federal finding of the cause of that accident.

A derailment last year near Boyds was blamed on a broken coupler.

The National Transportation Safety Board and railroad administration specialists looking into Saturday's derailment are focusing on a worn track switch that they suspect diverted one set of freight car wheels off the main line as the train was traveling south at 55 mph.

An additional 11 cars on the 90-car train derailed, crashing into each other, a trackside warehouse and a Metro electrical power station. Both inbound and outbound Red Line tracks were severed.

The safety board also has found that the wheels riding on the outside rail on the car that first derailed were more worn than those on the inside rail. Investigators say that worn wheels could have been more susceptible to derailment.

The wreck caused no injuries, but the possibility of a similar derailment causing a rush-hour catastrophe has triggered renewed calls for Metro and CSX to take action to reduce the risks on the 6.5 miles of corridor they share between Union Station and Silver Spring. Metro board members, legislators and some federal safety experts have suggested that CSX limit the lengths, speed or schedules of the 14 or so freight trains it runs every day along that line.

A safety board special study of "common corridor dangers" will examine these and other options, such as widening the distance between tracks or erecting barriers between Metro and CSX tracks. The only barrier now is a chain-link fence.

About 5,500 riders used the temporary shuttle buses during yesterday's morning rush, said Metro spokeswoman Beverly Silverberg. On a typical weekday morning, about 9,500 Metro riders board at the Silver Spring station, and about 3,500 board at Takoma.

Morning commuters also can ride between Silver Spring and Union Station today on six rush-hour Maryland Rail Commuter Service trains, a commuter spokesman said.