TAMPA, Florida (Reuters) - Republican Mitt Romney is turning to an experienced hand to play the role of President Barack Obama in debate preparations: Senator Rob Portman of Ohio, a campaign official said.

Romney and Obama will face off in three presidential debates this fall.

Romney has begun some early debate preparations, talking over subjects with top aides. But when he gets more serious and has an actual practice debate, Portman will stand in as Obama to represent the Democrat's views.

Portman is revisiting a role he played in 2008 when he played Obama in debate prep for that year's Republican nominee, Senator John McCain.

Portman was on Romney's vice presidential running mate short list before Romney selected Wisconsin Congressman Paul Ryan as his No. 2.

(Reporting by Steve Holland; Editing by Alistair Bell and Leslie Adler)