The Norfolk Southern Corp. train derailment that injured 214 passengers in Suffolk, Va., last year was caused by the company's failure to train and supervise properly the employes who repaired and inspected the track before the accident, federal safety officials said yesterday.

A section of track and a track switch had been displaced during repairs at the site of the May 18, 1986, accident, in which 14 of 23 passenger cars derailed, according to the National Transportation Safety Board report adopted yesterday.

The derailment occurred on an isolated stretch of track running through Great Dismal Swamp, a 106,000-acre wildlife refuge. The westbound train was carrying employes and their guests on a company outing from Norfolk to Petersburg and back.

The train was pulled by a steam locomotive operated by Robert B. Claytor, who was chairman and chief executive of Norfolk Southern at the time but has since retired. "The operation of the train was not a causal factor in the derailment," the safety board concluded.

Although there was no indication that drugs were involved in the accident, the safety board recommended that the Federal Railroad Administration alter its rules to require testing in derailments causing serious injuries.

Claytor, who is a qualified engineer, was not tested for drugs after the derailment because the accident did not meet federal criteria, which require toxicological tests in the event of a death or damage exceeding $500,000. Damage in the accident was estimated to be $258,500.

Safety board Vice Chairwoman Patricia A. Goldman emphasized that there was "no reason to suspect" that drugs were involved. "The problem is that testing is not automatic."

Norfolk Southern officials declined to comment because they had not seen the safety board's final report yesterday, a spokeswoman said.

The safety board found that the track was first misaligned shortly before the accident when a piece of track maintenance equipment damaged a track switch. The track foreman responsible for the maintenance operation "received minimal instructions" and was supervising "without a clear understanding of what was expected," the board wrote.

Subsequent repair work on the switch left the track misaligned in the approach to the switch.

The track inspector who checked the rails had not performed federally required track inspections in nine years and "was not aware of the repairs and resultant track alignment problem," the report said. "His failure to know the class of track inspected, his inability to interpret his reports, and his perception of kinks in the track was a reflection of his lack of qualifications and training."

After blaming the company for inadequate training and supervision of its maintenance workers, the safety board recommended that the railroad "develop and implement a program" to provide better training. The safety board staff said that Norfolk Southern is developing a new program.

The safety board also recommended that the Federal Railroad Administration require periodic checks to make sure that maintenance workers and inspectors continue to be qualified to do their jobs.