WASHINGTON — Saying that safety practices at General Motors were “broken,” federal regulators on Friday imposed the biggest punishment they could on the automaker and condemned it over its failure to promptly report a defect that G.M. has linked to 13 deaths.

G.M. will pay a $35 million penalty — the maximum allowed and the largest ever imposed on an automaker — and will be required to make wide-ranging changes to its safety practices that will be supervised by the government, another first for an automaker.

“What G.M. did was break the law,” Anthony Foxx, the secretary of transportation, said at a news conference.

The investigation found “deeply disturbing” evidence over how G.M. treated safety concerns, said David Friedman, who works under Mr. Foxx as the head of the National Highway Traffic Safety Administration.