The Firestone Tire & Rubber Co. has put its entire stock of the discontinued Firestone 500 steel-belted radial automobile tire on sale at half price at the same time the tire is being investigated by a federal agency for safety defects.

A consumer group, The Naperbacked Center for Avco Safety, fueled the controversy yesterday by releasing a report blamming defects in the tire for five deaths and six serious injuries since last November.

Firestone officials acknowledged the sale, which is being conducted in Florida and other southern states. They further said that they had no intention of halting the sale because they believe the tire to be safe.They blamed the incidents reported on improper maintenance of the tire by owners.

The decision to continue selling the tire reportedly angered Rep. John Moss, (D-Calif.), who heads the House Subcommittee on Oversight and Investigations. Committee sources said he may call for congressional hearings.

Three days ago, before learning of the sale, Moss sent a letter to Firestone asking the firm to look into "reported high failure rates in these tires." The letter also asked the company why many retailers have refused to handle the tires.

Yesterday, after learning of the sale. Moss said, "Firestone owes the public more than a statement, in effect blaming the reported accidents, injuries and fatalities on the users of Firestone tires."

Firestone spokesman James Strandberg contended yesterday that. "With proper care, the tire is safe, and will give long mileage and service."

He acknowledge that the sale was taking place in the South and said it would continue, adding that he had indications the tires were selling well "because they're good tires and literally million of them are running useful lives."

Firestone stopped making the 500 radial last year, but in March the National Highway Traffic Safety Administration announced that it was investigating the tire for defects because it had received more than 500 consumer complaints about blowout and tread separations.

Firestone went to federal court in Cleveland to prevent NHTSA from distributing the results of a study indicating a sharply higher amount of complaint about Firestone tires than about all other brands listed.

The company said the study was unfair and based on hiased information. U.S. District Court Judge John Manos in Cleveland issued a temporary restraining order preventing NHTSA from distributing the study. Manos is now attempting to discover the source of a leak of the report to the Center for Auto Safety, which later published the results.

The report revealed that Firestone steel-belted radials have higher failure rates than those of five other major tire manufacturers, with one half of the Firestone owners who responded to the survey complaining about their tires.

Goodrich, Goodyear and Uniroyal tires generated complaints about by one-third of their owners, General by one-fourth, and Michelin by only about 2 per cent of their owners.

In a letter sent by Clarence Ditlow of the Center for Auto Safety to Firestone on Tuesday of this week, Ditlow accused the tire firm of a "callous display of corporate disregard for human life and safety" by selling the remaining 500's at bargain prices while the investigation goes on.

Ditlow's letter details the description of five deaths in two auto accidents since the center announced its own investigation into Firestone last November.

Firestone has contended that many of the accidents or problems could have been caused by improper inflation of the tires, or other improper maintenance.

But in Ditlow's letter, he describes an accident last November in which "four parents of two El Paso, Texas, families were killed when a Firestone 500 blew out on the 1976 Ford station wagon in which they were riding. An eyewitness truck driver saw the right rear Firestone 500 blow out, causing the station wagon to roll over, killing its occupants. The tires were checked for air pressure 24 hours before the accident . . . The parents are survived by eight children."

Meanwhile, 15 persons reportedly were subpoenaed by Judge Manos this week in his efforts to discover who leaked the original NHTSA report to the consumer group and the media.

A Washington-based reporter for Knight-Ridder Newspapers, two reporters for the industry paper Rubber and Plastic News, and 12 NHTSA officials have been subpoenaed to appear before Manos, according to the Akron Beacon-Journal, the Knight-Ridder newspaper that ran one of the first stories on the study.