The 64-year-old is scheduled to make the announcement during the Fourth of July holiday in Nashville, and a fundraising committee will begin work next Monday, the advisers said.

However, campaign spokesman Mark Corallo said Thompson, R-Tenn., could still decide not to run or to postpone the announcement.

Thompson's top rivals -- Rudolph Giuliani, John McCain and Mitt Romney -- have a significant fundraising advantage for the current quarter, although the report said Thompson spent Tuesday afternoon in a conference call with more than 100 potential donors, each of whom was asked to raise about $50,000, the report said.

Since Thompson began hinting he might get in, polls have generally showed him tied for third with Romney, the report said.