Republican Senator John McCain is preparing to launch his bid to be US president in 2008.
John McCain is well known by the American voters
Mr McCain will file paperwork for an exploratory committee, the first step in any campaign for the White House.
Exploratory committees are used to examine issues including how much campaign finance a candidate can raise.
The Arizona senator will be the second high-profile Republican to declare an interest in the presidency, after ex-New York Mayor Rudolph Giuliani.
Mr McCain has been widely tipped to run for the White House for some time.
He is a well-known figure across the US, who recently campaigned against the torture of terror suspects in US custody.
He campaigned vigorously for other Republican candidates during the run-up to the recent mid-term elections, raising his profile while remaining independent of President Bush.
Mr McCain narrowly lost out to Mr Bush for the Republican nomination ahead of the 2000 election.
A former military man, Mr McCain was famously held as a prisoner of war during the Vietnam war.
His embryonic campaign team launched a website to accompany the establishment of the committee, containing a lengthy biography of the would-be candidate.
The move was widely expected, but Mr McCain insists he will not make any final decision on whether to run until the end of December.
Tommy Thompson, a former governor of Wisconsin who served in President George W Bush's first administration, also plans to set up a committee, reports say.