Washington ? Congress members on Monday accused Toyota officials of making misleading public statements about the causes of its runaway cars and faulted federal safety regulators for conducting “cursory and ineffective” investigations because of a crippling lack of expertise.

The charges from House members amplify the unprecedented scrutiny focused on the beleaguered automaker and the National Highway Traffic Safety Administration. In addition to three congressional committees, which are holding hearings beginning today, a federal grand jury has subpoenaed company documents relating to unintended acceleration, and so has the Securities and Exchange Commission, Toyota announced Monday.

The allegations Monday from Energy and Commerce Committee members frame what is expected to be one of the key questions before lawmakers, as well as consumers: Has Toyota really made its cars safe by recalling interfering floor mats and sticky pedals, as it has said repeatedly, or does the cause of the unintended acceleration episodes go deeper into engine electronics?

Congressional investigators, along with safety advocates, victims’ families and trial lawyers, are skeptical of Toyota’s explanations. They think there is a problem in the electronic throttle systems.

The letters Monday from Rep. Henry Waxman, D-Calif., and Rep. Bart Stupak, D-Mich., to James Lentz III, president of Toyota Motor Sales USA, and Transportation Secretary Ray LaHood accused Toyota and federal safety regulators of overlooking evidence as far back as 2004 that the automaker’s engine electronics had defects that could be causing unintended acceleration.

In June 2004, the automaker and NHTSA officials discussed a chart showing that Toyota Camrys with new electronic throttles had 400 percent more complaints regarding “vehicle speed.”

Moreover, according to investigators, Toyota could have seen from its database of consumer calls that floor mats and sticky pedals didn’t explain all the reports of unintended acceleration. Approximately 70 percent of the sudden unintended acceleration events in Toyota’s customer database involved vehicles that are not subject to recalls.

“Yet despite these warnings, Toyota appears to have conducted no systematic investigation into whether electronic defects could lead to sudden unintended acceleration,” the Waxman and Stupak letter to Lentz said.

The investigators also noted that in a Feb. 5 letter, a Toyota attorney reported to the committee that the causes of sudden unintended acceleration are “multiple” and “hard to identify.”