WASHINGTON — Under withering questioning from a congressional committee Tuesday, a top Toyota executive said the automaker still hasn’t ruled out electronics as a potential cause of sudden acceleration, acknowledging that fixing floor mats and sticking pedals would ”not totally” solve the problem.

Speaking before the House Commerce and Energy Committee for more than two hours, James E. Lentz, Toyota’s top U.S. sales executive, apologized for what he said was poor communications inside the company and with its customers that led to the recall of nearly 10 million vehicles.

”The two fixes solve the problems that we know of,” said Lentz, noting that the company was awaiting results of two studies on whether electronics in Toyota and Lexus vehicles could cause them to accelerate out of control.

His testimony came in the first of three congressional hearings called to investigate how Toyota and federal safety officials handled the sudden acceleration problem. Other Toyota officials, including Chief Executive Akio Toyoda, are scheduled to appear Wednesday and early next week.

In response to what he characterized as a communications breakdown between customers and company safety engineers, Lentz told the committee that the automaker would soon implement a ”SWAT team” of specialists who would investigate vehicles with safety troubles within 24 hours.

In addition, the company plans to install an electronic program that allows the brake to override the throttle on a larger number of its vehicles than previously announced, but stopped short of promising to install it on all of the millions of Toyota vehicles already on the road.

His remarks about the potential causes go to the heart of the congressional investigators’ concern on the problem of sudden acceleration and how Toyota has responded to the safety crisis. The panel, a subcommittee of the House Energy and Commerce Committee, also is looking at how U.S. regulators from the National Highway Traffic Safety Administration dealt with the company.

Did the recall solve the problem, asked committee Chairman Henry Waxman, D-Calif.

”Not totally,” Lentz replied, but he added that the recall would resolve the bulk of the issue.

In a day of hearings, the panel also heard from motorists forced to deal with the acceleration and safety experts who questioned whether the mechanical repairs would fix the problem.

In a tearful recounting, Rhonda Smith of Sevierville, Tenn., told the panel how her Lexus dangerously and suddenly sped up to 100 mph in 2006.

”I prayed for God to help me,” Smith said as she recalled how she pumped the brakes. Finally, she called her husband. ”I knew he could not help me, but I wanted to hear his voice one more time.”

When the vehicle finally dropped to 35 mph, Smith said she was finally able to turn off the engine. Smith was especially caustic about the brakes.

”Shame on you, Toyota,” she said.

”I’m embarrassed for what happened,” Lentz said of Smith’s ordeal. He said Toyota is putting in new brakes that can override the gas pedal.

Toyota President Toyoda, who will testify Wednesday, will take responsibility for Toyota’s safety woes and will apologize to any motorist who had to deal with sudden acceleration, according to his prepared remarks.

Toyoda is expected to offer condolences to a San Diego family killed in late August. It was that accident that helped lead to the current congressional investigation.