DETROIT — The Transportation Department said Monday it would seek a $16.4 million fine against Toyota, the largest allowed, because the company had failed to promptly notify the government about potential problems with accelerator pedals.

The fine, which Toyota has two weeks to contest, would be the largest civil penalty assessed by the government against a car company. In taking the step, federal authorities are sending the strongest signal yet that they believe the carmaker deliberately concealed safety information from them.

“We now have proof that Toyota failed to live up to its legal obligations,” Transportation Secretary Ray LaHood said in a statement. “Worse yet, they knowingly hid a dangerous defect for months from U.S. officials and did not take action to protect millions of drivers and their families.”

Mr. LaHood said documents obtained by the department showed Toyota had known of the potential pedal defect since at least last Sept. 29, when it issued repair procedures in 31 European countries and Canada to address complaints that accelerator pedals could stick and cause sudden, unintended acceleration.