Scientists and climate policy advocates around the world say they are watching the administration’s global warming actions and statements with deep worry. Many reacted with deep concern to Mr. Pruitt’s remarks this month that he did not believe carbon dioxide was a primary driver of climate change, a statement at odds with the global scientific consensus. They also noted the remarks last week by Mick Mulvaney, the director of the White House Office of Management and Budget, in justifying Mr. Trump’s proposed cuts to climate change research programs.

“As to climate change, I think the president was fairly straightforward: We’re not spending money on that anymore,” Mr. Mulvaney said at a White House briefing.

“The message they are sending to the rest of the world is that they don’t believe climate change is serious. It’s shocking to see such a degree of ignorance from the United States,” said Mario J. Molina, a Nobel Prize-winning scientist from Mexico who advises nations on climate change policy.

The policy reversals also signal that Mr. Trump has no intention of following through on Mr. Obama’s formal pledges under the Paris accord, under which nearly every country in the world submitted plans detailing actions to limit global warming over the coming decade.

Under the accord as it stands, the United States has pledged to reduce its greenhouse pollution about 26 percent from 2005 levels by 2025. That can be achieved only if the United States not only implements the Clean Power Plan and tailpipe-pollution rules, but also tightens them or adds more policies in future years.

“The message clearly is, ‘We won’t do what the United States has promised to do,’” Mr. Molina said.

In addition to directing Mr. Pruitt to withdraw the Clean Power Plan, the draft order instructs Attorney General Jeff Sessions to request that a federal court halt consideration of a 28-state lawsuit against the regulation. The case was argued before the United States Court of Appeals for the District of Columbia Circuit in September, and the court is expected to release a decision in the coming months on whether to uphold or strike down the rule.