EPA chief Gina McCarthy said Wednesday that the Obama administration is finished waiting for Congress to act on climate change and plans to bypass the legislative branch in developing a federal response.

Ms. McCarthy, who was confirmed last month as Environmental Protection Agency administrator, cited President Obama’s June 25 speech at Georgetown University, in which he unveiled his Climate Action Plan and vowed to make combatting climate change a priority of his second term.

Mr. Obama gave “what I really think is a most remarkable speech by a president of the United States,” said Ms. McCarthy in remarks at the University of Colorado Boulder.

“Essentially, he said that it is time to act,” she said. “And he said he wasn’t going to wait for Congress, but that he had administrative authorities and that it was time to start utilizing those more effectively and in a more concerted way.”

She insisted that reducing greenhouse-gas emissions could be accomplished without harming economic growth, calling the tension between the two priorities a “false choice.”

“We’re going to do this this year, next year, the following year, until people understand these are not scary things to do, these are actions we can all do, they’re actions that benefit everybody, that will grow the economy, and they’re actions that will protect the health and safety of individuals,” Ms. McCarthy said.

The president’s Climate Action Plan has come under criticism from Republicans, led by Senate Minority Leader Mitch McConnell of Kentucky, who said in June the plan amounted to a “war on coal” and a “war on jobs.”

“It’s tantamount to kicking the ladder out from beneath the feet of any Americans struggling in today’s economy,” Mr. McConnell said.

In 2009, Congress rejected a bill to establish a cap-and-trade system designed to discourage greenhouse-gas emissions. That measure, known as the Waxman-Markey bill, passed the House but was defeated in the Senate at a time when Democrats controlled both houses.

Mr. Obama’s plan comes after years of criticism from environmentalists who have faulted him for a lack of attention to global warming. The plan includes reducing carbon pollution from power plants, accelerating green-energy permitting, and increasing fuel-economy standards.

Ms. McCarthy said Colorado and Boulder are examples of jurisdictions that have taken positive action.

“[The president] told us to start paying attention to what’s going on in states and cities like Colorado and Boulder, and to start learning what you have already learned and to start getting the federal government to take the responsibility that it must take to face the challenge of climate change,” she said.

She didn’t list specific actions, but in June the Boulder City Council voted to enact a one-year moratorium on hydraulic fracturing, a procedure used to extract petroleum and natural gas from the ground.

The Colorado legislature passed a bill earlier this year to double the renewable-energy standard on rural communities, prompting a backlash against what critics have dubbed “the war on rural Colorado” and launching a movement by lawmakers in a dozen northern counties to explore forming their own state.

Ms. McCarthy’s remarks came prior to a panel discussion featuring former Colorado Gov. Bill Ritter, Colorado Oil and Gas Association President Tisha Schuller, and Brad Udall, director of the Getches-Wilkinson Center for Natural Resources, Energy and the Environment at the University of Colorado School of Law.