Ford Motor Co. and its CEO Jacques Nasser found themselves on the hot seat Tuesday as lawmakers raised safety concerns about the company's replacement of millions of Firestone tires and the government said it may probe its hugely popular Explorer sports utility vehicle.

The joint House subcommittee hearing was called to sort out claims from warring former partners Ford and Bridgestone/Firestone over responsibility for 203 deaths and more than 700 injuries linked to blowouts of Firestone tires. Those tires were fitted mostly as standard equipment on the Explorer.

House members wasted no time in aggressively questioning Nasser on the scope and thoroughness of the replacement of as many as 13 million Firestone Wilderness AT tires on all its vehicles.

Nasser vigorously defended the company's commitment to safety and expressed confidence in its data and analysis that he said justified the dramatic move.

"We're taking all the Wilderness AT tires off the road," he said. "If anything, we may have overreached because of the need to install some confidence back in the marketplace. I'm hoping we've done that."

Congressional investigators also indicated that Ford may be replacing Firestone tires on its vehicles with other brands that have even higher failure rates.

Rep. Billy Tauzin, R-La., chairman of the House Commerce Committee, disclosed at the hearing that congressional investigators have analyzed the failure rates of replacement tires Ford is using and found some fail more often than the Firestone Wilderness AT tires Ford recalled last month. The replacement tires are made by Michelin, Continental, Goodyear, General, BF Goodrich and Uniroyal.

"Ford is going to replace these recall tires with tires that have a worse claims history than some of the tires that are coming off the Explorers," Tauzin said.

He said House investigators have learned that one of the replacement tires has a claims rate of 124 per million tires, well in excess of the five claims per million rate that Ford cites in its recall.

Nasser asked for Tauzin's data to be made public, but Tauzin refused, saying he wanted federal highway safety officials to take 30 days to look at the information.

Ford does not have access to the same information because tire makers keep their property damage claims rates confidential. The Commerce Committee has been collecting that information from tire makers for several months.

Explorer Inquiry?

Separately, a Transportation Department official said in written testimony delivered to Congress that NHTSA is considering an investigation of the Explorer in addition to its investigation of whether to expand the Firestone recall.

Michael Jackson, deputy transportation secretary, said regulators are conducting an analysis to determine if a formal investigation is warranted. "The department and NHTSA are giving this matter full consideration," Jackson said.

Nasser defended the Explorer, saying criticism challenging its safety is not based on fact. "Real world data shows that the Explorer is among the safest SUVs on the market," he said.

The Wilderness AT has been at the center of a nearly yearlong debate over the safety of Firestone tires.

The Wilderness AT has been standard equipment on the Ford Explorer, the world's best-selling sport utility vehicle. Many of the 203 fatal accidents among the thousands of crashes reported to the highway safety administration in the last year were rollovers of the Explorer that occurred after the tires failed.

Warring Companies

Ford insists the problem is the result of flawed tires, but Bridgestone/Firestone says the design of the Explorer also is a factor.

Bridgestone/Firestone Inc.'s voluntary recall of 6.5 million tires last August included the 15-inch version of the Wilderness AT, made at its plant in Decatur, Ill.

The company insisted that other sizes of the tire made at other plants were safe. But last month Ford said it was concerned about safety and announced it would replace all 13 million Wilderness ATs still on its vehicles.

A day earlier, aware of the impending announcement, Bridgestone/Firestone ended its 96-year relationship with Ford.

John Lampe, chief executive of Bridgestone/Firestone Inc., said Ford's tests were "grossly unscientific and must be disregarded."

"We have had a growing and ultimately overwhelming conviction that tire design and manufacturing issues alone simply cannot account for what has been happening to the Explorer," Lampe said in a prepared statement.

Lawmakers called on NHTSA to quickly finish its investigation. "We have a corporate schoolyard brawl breaking out here," said Rep. Edward Markey, D-Mass. "We need an independent referee."

-- Reuters and the Associated Press contributed to this report.