ATLANTA - A federal judge ruled Thursday that airlines and other companies in the industry that are being sued by families of terrorism victims can't question FBI agents about the Sept. 11, 2001, attacks.

The defendants wanted to depose the agents and sought access to other evidence related to the investigation of the attacks that killed nearly 3,000 people in order to show at trial that the government's failure to catch the terrorists and prevent the attacks mitigates and excuses any alleged fault on the aviation companies' part.

The government objected.

The ruling by U.S. District Judge Alvin Hellerstein said the defendants have also argued that the terrorists likely would have succeeded even if the defendants had exercised due care.

"The issues to be tried relate to the acts and omissions of the aviation defendants, not the government," Hellerstein wrote in his ruling. "The government's failures to detect and abort the terrorists' plots would not affect the aviation defendants' potential liability."

There was no immediate comment from the defendants or their lawyers. Spokespersons for UAL Corp.'s United Airlines, AMR Corp.'s American Airlines and US Airways Group Inc. declined to comment. Lawyers for several airlines did not immediately return calls seeking comment. Other defendants include Delta Air Lines Inc., Continental Airlines Inc., AirTran Airways, Boeing Co. and several airport authorities and security companies.

The judge said he plans to set a trial date for the lawsuits involving three wrongful death cases and 19 property damage cases on July 28.

Many relatives of victims of the attacks received money from a special national fund established to compensate victims' families, though some relatives chose to sue instead.

The lawsuits claim negligence on the part of the defendants and seek to recover damages for injuries and fatalities, property damage and business loss that occurred as a result of the attacks. According to court papers, the plaintiffs have alleged or have indicated they are likely to allege that the aviation companies should have anticipated that terrorists would hijack planes and crash them into buildings in coordinated suicide attacks, and that the defendants should have put in place security procedures to effectively defend against such attacks.

The government urged the judge to block the aviation companies from interviewing six current and former FBI employees who the companies say would be able to testify as to what intelligence the FBI, CIA, Federal Aviation Administration and airlines had before the attacks regarding the terrorists' plans and capabilities, as well as how the entities shared and exploited the intelligence.

The government argued that it would be impossible to interview the employees without disclosing classified or privileged material that could cause serious damage to national security and interfere with pending law enforcement proceedings.

The largest investigation in FBI history has resulted in 167,000 interviews and more than 155,000 pieces of evidence and involved the pursuit of 500,000 investigative leads, the government noted.

The government said the FBI has turned over more than 33,000 pages of information to the aviation industry lawyers, including more than 10,000 pages of laboratory pictures and related information, witness interviews and descriptions of the hijackers' weapons.

The airlines and aviation companies have said they are defending themselves against lawsuits seeking billions of dollars in damages for injuries, fatalities, property damage and business losses related to the attacks.

The companies filed separate lawsuits against the CIA and the FBI seeking to force terrorism investigators to say whether the aviation industry was to blame for the Sept. 11 attacks.

Lawyers for the victims of the attacks have said the FBI should not be forced to provide more information.

In Thursday's ruling, the judge also denied the aviation defendants' motion for an order that the 9/11 commission's report as a whole, a staff monograph and selected staff statements, are relevant to the lawsuits. He said specific portions of the report may be admissible.

As to a motion by the defendants seeking to have testimony given by FBI agents during the trial of Sept. 11 conspirator Zacharias Moussaoui admitted in the lawsuits case, the judge granted the motion only as to the testimony of two agents in which they recount 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 wrote.

Moussaoui, a French citizen, is serving a life sentence after pleading guilty to helping plan the attacks.