WASHINGTON — Gina McCarthy, the White House climate adviser, has told confidants that she has been frustrated by the slow pace of climate progress and intends to step down in the coming months, according to several people to whom she has spoken.

Ms. McCarthy, 67, who has served since the start of the Biden administration, was widely expected to remain in her position for about a year, friends and colleagues said Thursday.

President Biden asked her to stay on, according to one person familiar with Ms. McCarthy’s plans. Others who have spoken with her in recent days said Ms. McCarthy had denied to them that she was leaving imminently and had told associates that she had no definite date in mind. She is expected to be succeeded by her deputy, Ali Zaidi.

Ms. McCarthy did not respond to requests for comment on her plans, which were first reported by Reuters. Vedant Patel, a White House spokesman, called the reports “untrue.”

“We have no personnel announcements to make,” Mr. Patel said in a statement. “Gina and her entire team continue to be laser focused on delivering on President Biden’s clean energy agenda.”

Mr. Biden tapped Ms. McCarthy, who served as administrator of the Environmental Protection Agency under President Barack Obama, to helm his ambitious climate agenda, which calls for cutting the nation’s greenhouse gas emissions roughly in half by the end of this decade.

But his plans have been stalled in Congress because of unified opposition from Republicans as well as from Senator Joe Manchin III, Democrat of West Virginia, who represents a crucial swing vote in the evenly divided Senate.

Separately, Mr. Biden’s plans to use executive authority to enact tough new rules on greenhouse pollution from power plants and automobiles could be sharply limited by a forthcoming decision from the conservative-leaning Supreme Court.

In addition, the war in Ukraine has driven up gasoline prices, prompting Mr. Biden to take steps that are anathema to climate activists. He released a record amount of oil from the Strategic Petroleum Reserve, pleaded with oil and gas companies to do more drilling and temporarily loosened environmental rules to allow gasoline blended with ethanol to be sold during the summer months, when it is ordinarily banned because it can cause smog.

Those moves came as a landmark United Nations report was released in which top scientists from around the world warned that time is running out for nations to pivot away from fossil fuels or face a future of climate catastrophe.

One person described Ms. McCarthy as being in “beleaguered mode” and said she had been worried about the political and legal challenges facing the administration’s climate plans. Others said she had bemoaned the difficulties of traveling and being away from her husband.

Publicly, though, Ms. McCarthy has insisted that she remains optimistic about the chances that climate legislation will pass this year. At a recent event in Washington, she said she was “not naïve” about the challenges but added, “I think we will have a bill that will move this fall.”

When she worked in the Obama administration, Ms. McCarthy was a chief architect of the president’s historic and far-reaching climate change policies.

After the election of Donald J. Trump, Ms. McCarthy became head of the Natural Resources Defense Council, which sued the Trump administration more than 100 times as Mr. Trump countermanded much of Mr. Obama’s environmental legacy.

Under Mr. Biden, Ms. McCarthy was charged with leading a “whole-of-government” approach in which nearly every federal agency enacted new regulations designed to address climate change. She had also hoped to guide Congress toward passage of new climate laws that could not be rolled back by a future president, ensuring a steady drop in the nation’s greenhouse emissions.

Zolan Kanno-Youngs contributed reporting.