WASHINGTON — In his first three weeks on the job, Andrew Wheeler, the acting head of the Environmental Protection Agency, has sought to halt two major efforts by his predecessor, Scott Pruitt, to roll back environmental regulations, arguing that the policies are legally vulnerable, according to people who have heard his reasoning.

Mr. Wheeler’s actions signal a strategic shift at the E.P.A., an agency at the heart of President Trump’s push to strip away regulations on industry. Under Mr. Pruitt, who resigned July 5 under a cloud of ethics investigations, the agency pushed for ambitious but fast-paced rollbacks of environmental rules. At least a half-dozen of those have been struck down by federal courts.

Mr. Wheeler, a former coal lobbyist who served as Mr. Pruitt’s deputy, has brought a more disciplined approach to dismantling environmental rules. It is an approach that may take longer, but it may be more effective in standing up to the inevitable legal challenges.

Prof. Richard L. Revesz, an expert in environmental law at New York University, said Mr. Wheeler was “trying to be more careful and less sloppy” than his former boss. “By taking time to improve the quality of the legal justifications, Wheeler may ensure that E.P.A. won’t be subject to losing on certain types of policies,” Professor Revesz said.