Senator says US president has chosen ex-defence department deputy Ashton Carter as candidate for defence secretary.
Senator Jim Inhofe of Uklahoma said he was informed of the decision early on Tuesday.
Inhofe, the top Republican on the Senate Armed Services Committee, said he supports the choice of Carter to lead the Pentagon "very strongly".
If confirmed for the job by the Senate, Carter would replace outgoing US Defence Secretary Chuck Hagel.
Carter has support among Republicans who will take control of the Senate next month.
The 60-year-old has gained a reputation as an expert on hi-tech weapons and military budgets, portraying himself as a reformer intent on making the vast Pentagon bureaucracy more efficient.
While Carter is skilled in weapons programmes and technological trends, he has less experience overseeing war strategy and has never served in uniform - unlike Hagel who served in the military and was wounded in the Vietnam War.
An academic by training and a holder of a doctorate in theoretical physics from the University of Oxford, Carter worked in the Pentagon during Bill Clinton's presidency, overseeing nuclear arms policies and helped with efforts to remove nuclear weapons from Ukraine and other former Soviet territories.
A former professor at Harvard University's Kennedy School of Government, Carter served as the Pentagon's top weapons buyer from 2009 to 2011 and then as deputy defence secretary until 2013.