Nuclear power plants in the United States are not reporting some equipment failures to the government because of badly written rules, the inspector general of the Nuclear Regulatory Commission has warned.

Those rules, which are often contradictory, leave the commission without the muscle to enforce the federal law requiring the reporting of such problems, the inspector general said in a report issued Wednesday.

From December 2009 to September 2010, the report said, the commission found 24 instances in which equipment problems were not properly reported. If the rules are not improved, it said, they “could reduce the margin of safety for operating nuclear power reactors.”

The commission, which operates independently of the inspector general, countered in a statement that it “has a variety of other regulations that effectively encompass reporting all defects.” It added, “The N.R.C. continues to conclude plants are operating safely.”