WASHINGTON - Toyota Motor Corp. apologized for letting safety standards slip during a period of fast growth and vowed to respond more quickly to consumer complaints as two days of congressional hearings crucial to the automaker's reputation began, Reuters reported.

"We now understand that we must think differently when investigating complaints and communicate faster, better and more effectively with our customers and our regulators," said Jim Lentz, president of Toyota Motor Sales U.S.A. Inc.

Under questioning, Lentz agreed that 70 percent of complaints about unintended acceleration remained unexplained. "That is probably fair to say," he said during a 2-hour-and-15-minute grilling from lawmakers. "There are many factors that lead to it."

President Akio Toyoda, who will testify Wednesday, said in prepared testimony he was "deeply sorry" for accidents caused by safety problems with Toyota vehicles and detailed a set of reforms that would shift control of recall decisions away from the automaker's Japanese headquarters.

"We pursued growth over the speed at which we were able to develop our people and our organization, and we should sincerely be mindful of that," Toyoda said.

Lentz echoed that in his remarks: "The company's processes from top to bottom are being re-evaluated,” he said.