WASHINGTON (AP) _ The Labor Department today said it has issued six safety violations to two companies using the chemical involved in the Dec. 3 accident that killed more than 2,000 people in Bhopal, India.

But the Occupational Safety and Health Administration said that its inspections of all four major U.S. users of methyl isocyanate and the one U.S. manufacturing plant have determined that the facilities are safe. The use of backup safety systems virtually removes the possibility in the United States of a tragedy similar to that which occurred in Bhopal, the agency said.

''We can say that generally these five facilities are in rigorous compliance with OSHA standards,'' said Jane A. Matheson, deputy assistant secretary of labor.

Production of the chemical at the Union Carbide Corp. plant in Institute, W.Va., was halted after the Bhopal tragedy, so no production was taking place during OSHA's inspection. The agency will perform inspections when production resumes. OSHA has conducted 32 inspections of the Institute plant - 11 since 1980 - and no citations relating to the chemical were issued, said Ms. Matheson.

Four serious violations were found by OSHA at the FMC Corp. in Middleport, N.Y. The federal agency said an electric motor that was not explosion-proof was in use near storage tanks filled with the chemical; that a worker watered down a spill of the chemical without wearing proper protective clothing; that employees were using improper respirators near the chemical, and that there were improper engineering controls around a storage tank.

OSHA found two serious violations at Union Carbide's operation in Woodbine, Ga. One was for having ineffective relief devices connected with shutoff valves in potentially over-pressurized containers. The other was for improper engineering controls on an unloading system for the chemical.

The federal regulatory agency proposed fines of $2,920 at FMC and $1,280 at Woodbine.

The plants may contest the violations before the Occupational Safety and Health Review Commission.