A U.S. judge has denied a motion by a group of airlines to depose several Federal Bureau of Investigation agents regarding the government's probes into the Sept. 11, 2001, terrorist attacks in New York and Washington.

In an order Thursday, U.S. District Judge Alvin Hellerstein in Manhattan denied a motion by the airlines to question six current and former FBI agents, a potential setback for their defense.

The judge indicated the airline defendants hoped to show at trial that the government's failure to apprehend the terrorists and stop the attacks was so considerable that it mitigates and excuses any alleged faults of the airlines and the terrorists likely would have succeeded even if the defendants had exercised due care.

"The government's failures to detect and abort the terrorists' plots would not affect the aviation defendants' potential liability," the judge wrote. "Moreover, efforts to prove these propositions would cause confusion and prejudice, and burden court and jury with long delays and unduly lengthy trial proceedings."

The rulings relate to three wrongful death cases and 19 property-damage cases.

The defendants include units of UAL Corp. (UAUA), US Airways Group Inc. (LCC), Delta Air Lines Inc. (DAL), Continental Airlines Inc. (CAL) and AirTran Holdings Inc. (AAI).

A lawyer for the airlines didn't immediately return a phone call seeking comment Thursday.

The judge did allow some of the testimony of two of the FBI agents from the trial of Sept. 11 conspirator Zacarias Moussaoui, who is serving a life sentence - namely what they learned in their investigations.

"Testimony as to what their superiors did or did not do is not relevant, and is not admissible," the judge said.

The judge also denied a motion to admit the 9/11 Commission report as a whole as evidence in the case, instead only admitting the chronology provided in the report.

-By Chad Bray, Dow Jones Newswires; 212-227-2017; chad.bray@dowjones.com