The National Transportation Safety Board, saying it may have found the cause of the Virginia bus crash that killed 11 commuters last month, called yesterday for increased inspections of what it described as a "potentially hazardous" steering mechanism used in many large commercial vehicles.

Although the agency said it has not determined specifically what caused the bus accident, its investigation reported they found a key element in the wrecked bus's steering system was worn "to the extent that it may have caused" the driver to lose control of the vehicle.

The board said that particular attention should be given to buses and trucks with power steering, such as that of the 22-year-old D&J Transportation bus that ran off Interstate 95 and plunged 25 feet into a creek near Quantico on Feb. 18. The report tended to support the previously disclosed findings of investigators looking into the accident, the second worst bus accident in Virginia.

The D&J bus, the report said, "appeared to have been in relatively good overall mechanical condition at the time of the accident. Its tires were not excessively worn, brake linings were relatively new, brake adjustments were within acceptable limits and wear points were properly lubricated." The bus, it said, had been inspeced Jan. 29 and was "deemed roadworthy" by Virginia officials.

However, the report said, detailed inspection revealed that the "mating parts" of a ball joint assembly in the bus's steering mechanism were "severely worn. The accumulative wear was such that the ball could be pulled by hand, with little effort, through the ball seat and socket body . . . The Safety Board is concerned that this ball joint wear was not detected during routine vehicle maintenance or inspection, and it apparently did not manifest itself as a steering problem to the drivers of the bus."

Current steering inspection tests, established by the National Highway Traffic Safety Administration, include measurement of the amount of "free play" in steering mechanisms, the report noted. That standard is "probably acceptable for buses and trucks with mechanical steering systems," the board said.

But, it said, the design of power steering mechanisms on many trucks and buses, including the bus involved in the accident, "is such that a worn ball joint or end assembly will not be detected using the procedures described by the NHTSA standard."

Because of the "potential serious consequences" the board recommended that power steering assemblies should be visually inspected for free play, and then disassembled and inspected more closely.

The board also urged the National Highway Traffic Safety Administration to work with manufacturers to develop more stringent standards for steering system inspections.