The Justice Department said yesterday it is investigating allegations that an aircraft parts supplier in Missouri "falsely stated the condition" of parts sold to airlines and other customers, and the Federal Aviation Administration has warned airlines to check every part supplied by the company.

The FAA also has opened an investigation into whether to revoke the certificate held by K.C. Aerospace of Kansas City to act as a certified repair station.

On Aug. 15, the Federal Bureau of Investigation seized files and documents at the company's headquarters. Based on a preliminary examination of those documents, the FAA said it has alerted a number of airlines to check for possible bogus parts.

Richard Helfand, an attorney for K.C. Aerospace, said the government has told the company nothing about the investigation and that the firm is "in the dark" about details.

"We deny any of the allegations made by the Justice Department," Helfand said. He said the Justice Department announcement was a "highly irregular action" because it announced an investigation but did not accuse the company of any crime.

The announcement, which said that "K.C. Aerospace has neither been charged with nor convicted of any crime at this time," was unusual because it quoted Attorney General Dick Thornburgh as saying: "We must be constantly alert to allegations that involve tampering with the safety of the public. Such actions will not be tolerated, and any perpetrators will be prosecuted to the fullest extent."

The announcement said evidence will be presented to a grand jury in Kansas City.

An FAA spokesman said the government does not know how widespread the problem may be, but is developing information from the seized files to aid airlines in identifying parts that must be removed from aircraft and maintenance inventories.

However, an airline industry source said the parts were sold to "a lot of airlines. It's not just one or two."

K.C. Aerospace is one of hundreds of firms that supply parts and are certified by the FAA to act as repair stations. It is the aviation equivalent of an independent service station that also sells parts. Such firms often buy parts from airlines when, for example, an airline phases out one model of an airplane and has no further need for its inventory. The firms sell the thousands of airliner parts, both reusable, such as some engine parts, and nonreusable, such as nuts and bolts.

K.C. Aerospace, with 40 employees, is a certified repair station for airplane instruments and avionics -- the electronic equipment used on airliners.