WASHINGTON: President-elect Donald J. Trump moved quickly on Friday to begin filling national security posts at the top echelons of his administration, selecting a group of hawks and campaign loyalists who reflect the hard-line views that defined his run for president.

Mr. Trump said he would nominate as attorney general Senator Jeff Sessions of Alabama, who has been a fierce supporter of a crackdown on undocumented immigrants. The president-elect also moved to install Michael T. Flynn, a retired lieutenant general who has said that Islamist militancy poses a global existential threat, as his national security adviser. And as director of the C.I.A., Mr. Trump selected Representative Mike Pompeo of Kansas, who harshly criticized Hillary Clinton during the House investigation of the 2012 attack on the United States diplomatic compound in Benghazi, Libya.

All three are regarded, in some ways, as outliers from conventional Republican thinking, shunned at times for strident statements, controversial positions or highly partisan moves.

The flurry of announcements indicated that Mr. Trump was gaining control over a transition operation that had been entangled in infighting during its early stages.  

Transition officials said Mr. Trump would meet over the weekend with a broad array of potential cabinet members and other advisers as a signal that he wanted to build a diverse team, without regard to political affiliation or support for his presidential bid. 

Among them are Mitt Romney, the 2012 Republican nominee and one of his party’s harshest critics of the president-elect’s campaign, who is a contender for secretary of state, and Michelle A. Rhee, a Democrat who pursued sweeping reforms during her controversy-filled tenure as the District of Columbia’s chancellor of schools. 

Mr. Trump also planned to meet on Saturday with James N. Mattis, a retired Marine Corps general who headed United States Central Command and is being considered for secretary of defense.