If confirmed by the Senate, Max Baucus would replace Ambassador Gary Locke, who announced last month he was stepping down. (Agencies)
There was no immediate comment from the White House on the disclosure, which was made by officials who spoke on condition of anonymity because they were not authorized to discuss the nomination publicly before a formal announcement.
Kathy Weber, a spokeswoman in Baucus' office, declined to confirm the move.
Baucus, 72, was first elected to the Senate in 1978, and since early 2007 has been chairman of the Senate Finance Committee. The panel has jurisdiction over taxes, trade, health care and more.
If confirmed before the end of next year, Baucus would resign his seat and create a vacancy, which Montana Gov Steve Bullock, a Democrat, would fill. A top candidate would likely be Lt Gov John Walsh, who has announced his candidacy to run for the seat.
If confirmed by the Senate, Max Baucus would replace Ambassador Gary Locke, who announced last month he was stepping down.