The Justice Department said yesterday that Federal Aviation Administration air traffic controllers handling Korean Air Lines Flight 007 had no way of knowing that the flight was straying off course, ultimately to be shot down by Soviet fighters Sept. 1, 1983, killing all 269 people on board.

The statement, in U.S District Court papers, came in the civil lawsuit brought by the families of the victims against the airline, the U.S. government and others.

The plaintiffs' recording expert said that air traffic control tapes contain the words "We should warn him" as background conversation. The words are heard as a controller in Anchorage was having trouble communicating with Flight 007, the plaintiffs say.

The controller was seeking a radioed position report from Flight 007. Although direct contact was not established, Flight 007 subsequently relayed its position report through another KAL plane, a circumstance the FAA has said is not unusual.

The communication difficulty occurred five hours before the plane was shot down, but the plaintiffs contend that it had already strayed far enough off course to be warned.

The Justice Department included an affidavit from FBI special agent Bruce E. Koenig, a tape expert. Koenig said, "Any statement . . . regarding what words are in the background conversation . . . would be pure and unwarranted speculation. I do not believe that anyone can state to even a reasonable degree of scientific certainty what is said."

The Justice Department denied that the controller was observing a radar screen carrying an Air Force radar return that showed the flight's position. It also denied that Air Force radar trackers had told controllers Flight 007 was straying.

Further, the department said, at the time that plaintiffs allege the plane was demonstrably off course, it was beyond the range of military radar.

"The evidence is clear that the controllers at Anchorage had no way of knowing that the aircraft was not where its pilot said it was," the department said. "Plaintiffs' offering of what must surely be the most convenient interpretation of background conversation imaginable does nothing to change this."

Donald W. Madole, lead attorney for the plaintiffs, declined to comment.