The Nuclear Regulatory Commission has ordered nearly 40 nuclear power plants nationwide to inspect pipes and fittings on which suppliers are alleged to have falsified test reports, the NRC said Thursday.

Some of the suspect flanges and fittings are used in safety-related systems, whose failure could thwart the shutdown of a reactor in an emergency, Edward Baker, an NRC section chief, said by telephone from Bethesda, Md.In some plants, the materials are in high-radiation areas, he said.

"The fact that (the plants) are listed doesn't necessarily mean that the materials are not good. What it means is because of facts we have found, the materials are suspect," Baker said.

Plants that received the materials have been ordered to replace them if necessary under an NRC bulletin being sent to the owners of 38 reactors this week. Plants in most cases must complete the work during their next refueling.

Plants under construction must comply with the NRC bulletin before they can load fuel. The Seabrook plant in New Hampshire is on the list; it is loaded with fuel but unlicensed because of emergency-planning roadblocks.

The NRC said the suspect piping came from Piping Supplies Inc. of Folsom, N.J., and West Jersey Manufacturing Co. of Williamstown, N.J. West Jersey went out of business in 1985, and company officials formed Piping Supplies, Baker said.

Piping supplied by the companies since 1976 is suspect, he said.

Baker said the companies claimed in test reports that the piping met standards set by the American Society of Mechanical Engineers, but in many cases could not provide documentation.