Toyota said Wednesday it would have to fix the gas pedals of about four million vehicles, including the Camry, to resolve a widespread problem with unintended acceleration. The announcement was another setback for Toyota, which until last year appeared all but unstoppable. Its disciplined business approach, surging profits and reputation for quality helped it take market share from troubled competitors, and win from General Motors the title of world’s largest automaker.

But the global downturn has battered Toyota, along with most car companies. And Toyota, which has issued other recalls in recent years, risks losing its standing in the eyes of many consumers as the benchmark for reliability. Three weeks ago, the company said it would recall only driver-side floor mats, which it said could get stuck on the accelerator and cause an accident. Since then, federal regulators have pressured Toyota to do more to insure the safety of several models, including the Camry, three Lexus sedans and its Prius hybrid.

Safety experts said the huge recall could do more damage to Toyota's reputation, much as Ford and Firestone suffered from rollover problems earlier this decade with the Ford Explorer. "Clearly Toyota has its back up against the wall like it never has before," said Sean Kane of Safety Research and Strategies, a consulting firm in Rehoboth, Mass.

The National Highway Traffic Safety Administration started scrutinizing the issue of jammed gas pedals after a high-speed crash in August near San Diego. A Lexus ES350 hit another vehicle at more than 120 miles per hour, killing four people. Moments before the crash, a passenger called 911 and said the gas pedal was stuck and the driver could not stop.