President Trump on Wednesday unilaterally weakened one of the nation’s bedrock conservation laws, the National Environmental Policy Act, limiting public review of federal infrastructure projects to speed up the permitting of freeways, power plants and pipelines. In doing so, the Trump administration claimed it would save hundreds of millions of dollars over almost a decade by significantly reducing the amount of time allowed for completing reviews of major infrastructure projects.

The president announced the final changes to the rule at the U.P.S. Hapeville Airport Hub in Atlanta, making the case that “mountains and mountains of red tape” and lengthy permit processes had held up major infrastructure projects across the country, including a lane expansion to the perpetually clogged Interstate 75 in Georgia. “All of that ends today,” he said. “We’re doing something very dramatic.”

Revising the 50-year-old law through regulatory reinterpretation is one of the biggest — and most audacious — deregulatory actions of the Trump administration, which to date has moved to roll back 100 rules protecting clean air and water, and others that aim to reduce the threat of human-caused climate change.