Arizona state officials complained of treads separating from Firestone tires fitted to light trucks and sport utility vehicles at least four years before the tire maker would tell federal regulators it was recalling 6.5 million tires for the same problems.

The Arizona Department of Administration on Monday released a letter it sent Bridgestone/Firestone dated July 22, 1996, asking for replacement the tires.

Firestone, a unit of Japan's Bridgestone Corp. <5108.t>, said it had replaced some tires on an individual basis in Arizona after receiving complaints from state officials, but denied there was any link with the current recall.

"We do not believe that the tread separations that were involved with the tires from three or four years ago are related at all to the current recall," said Phil Pacsi, director of consumer tires brand marketing for Bridgestone/Firestone.

"We believe that all of our other tires are safe," he said, noting the tires at issue in Arizona were a completely different model from the ones being recalled now.

The U.S. Senate Commerce Committee, chaired by Arizona Republican Sen. John McCain, will hold a hearing into the tire problems Tuesday.

On Aug. 9 this year, Firestone began recalling 6.5 million tires made up of certain 15-inch models of its ATX, ATX II and Wilderness AT tires in response to a federal probe of accidents now linked to at least 88 deaths.

Ford Motor Co. fitted the majority of the recalled tires to its Explorer sport utility and some light trucks.

As the investigation has progressed, the earliest date at which Firestone should have been aware of tread separation problems has steadily been pushed back.

But as when customer complaints from the Middle East were brought to Firestone's attention in 1988, the tiremaker concluded the Arizona problems would be explained by improper inflation and other abuse of the tires.

Arizona said in its 1996 letter to Firestone that it had Firehawk ATX tires on many state vehicles.

"This becomes a great concern since apparently the defect cause separation due to the high heat," the letter said. "We are currently in the hottest part of the year here in Arizona."

Katherine Babonis, support services branch chief for the Arizona Game and Fish Department, said on Monday that problems with the Firestone ATX tires were noticed in the summer of 1996.

A team of six Firestone engineers spent three days in September that year examining 175 agency light-duty pickup trucks at 11 locations statewide. As a result, 23 tires were taken out of service and 18 were taken for additional testing.

"They got back to us that the inflation was wrong or that we were using it off road," Babonis said.

Although the Firehawk ATX was not included in Firestone's voluntary recall, the National Highway Traffic Safety Administration included 10 sizes of Firehawk ATXs in a Sept 1 consumer warning about an additional 1.4 million suspect tires.

Firestone has so far refused to add these 1.4 million additional tires to its recall.