Mr. Trump’s choices for prominent national security jobs — attorney general, defense secretary, national security adviser, C.I.A. director — have already begun to more firmly establish the contours of his approach to foreign policy, even as he struggles to settle on someone to be the nation’s top diplomat as secretary of state.

On the domestic front, announcements of several cabinet posts are helping to define the new president’s approach to issues at home. His choices so far suggest a more conservative approach to many domestic issues than Mr. Trump himself articulated during the campaign.

This week, Mr. Trump is expected to fill a series of positions that will accelerate the U-turn from current policies.

He is said to be seriously considering Mary Fallin, Oklahoma’s Republican governor, for interior secretary, which would presage a shift away from the department’s current approach toward energy and public lands. Mr. Obama has aggressively sought to shut down fossil fuel production and increase the use of renewable sources of energy, while Ms. Fallin is an outspoken proponent of drilling and fracking on public lands. She was the first governor to announce she would oppose Mr. Obama’s proposed rules on emissions from coal-fired power plants.

Andrew F. Puzder, a wealthy California donor to Mr. Trump’s campaign whose company, CKE Restaurants, oversees chains such as Hardee’s, is said to be a leading candidate for labor secretary. Mr. Puzder has been extremely critical of the Obama administration’s labor policies, including its push for a higher minimum wage and for new overtime rules for workers.