It took the federal government 12 years to fulfill a congressional order that all underground coal mines be equipped with emergency breathing devices called self-contained self-rescuers. Now, two months later, an in-house study has turned up a potentially dangerous problem with some of the equipment.

More than a month after the report was issued, however, neither the Mine Safety and Health Administration nor the manufacturers of the respirators have notified mine safety directors of the problem, which could cause loss of consciousness.

An MSHA spokesman said the agency believed there "was only a remote possibility" that the problem could occur.

Researchers for the Interior Department's Bureau of Mines warned that some of the respirators do not have an automatic purge to rid the breathing circuit of nitrogen. If a miner exhales into the device before drawing his first breath, the report said, the bag will inflate with nitrogen and the oxygen demand valve will not be triggered.

The resulting drop in oxygen concentration could cause loss of consciousness "within a matter of minutes," according to the report. It urged that instruction manuals for two of the respirators be changed to emphasize the need to exhale before using the device.

Most of the mines have selected a device manufactured by Ocenco Inc. of Northbrook, Ill., which does not have an automatic nitrogen purge. Ocenco instruction manuals, the study said, "make no explicit demands" that the miner exhale before using the breathing device. The report also recommended that the manual for the respirator made by CSE Corp. of Monroeville, Pa., be changed, too.

A spokesman for Ocenco said it had agreed to modify its instructions, but was waiting for MSHA's approval before alerting mine safety directors.

An MSHA spokesman said CSE also had agreed to alter its training program.