Robert O. Work, a former top Navy official, is the leading candidate to become the next deputy defense secretary.
A source close to the confirmation process said congressional staffers have been told to prepare for his Senate nomination, which could run into tough questioning.
Mr. Work resigned as Navy undersecretary last spring and now runs the Center for a New American Security, a Democrat-leaning think tank.
“I am 100 percent certain Work is getting the nomination,” said the source, who requested anonymity to discuss the process.
Mr. Work, a retired Marine Corps colonel and strategist, would undergo Senate scrutiny on the Navy’s 30-year ship building plan, which military analysts say would construct too few vessels.
In addition, he could face questioning about a recent scandal in which senior Navy officers are accused of accepting financial favors from a port operator in Asia.
Former Deputy Defense Secretary Ash Carter stepped down earlier this month as the No. 2 Pentagon official, second to Secretary Chuck Hagel.
Christine Fox, a former Pentagon budget analyst, is serving as acting deputy defense secretary.
A White House official declined to comment.