WASHINGTON — The new Republican leader of the Securities and Exchange Commission has imposed fresh curbs on the agency’s enforcement staff, scaling back their powers to initiate investigations of alleged financial misdeeds.

The move by Michael Piwowar — named acting head of the agency in late January by the Trump administration — narrows actions launched during the Obama administration designed to make it easier for the Wall Street regulator to launch probes in the wake of the financial crisis and a series of colossal investment scandals.