The detention camp has long drawn international criticism
Barack Obama will issue an executive order within days of entering the White House to close the Guantanamo detention centre, senior advisers have confirmed.
Mr Obama, who is due to be inaugurated as US president on 20 January, has repeatedly promised to close the camp, where some 250 inmates remain.
The signing of the order is unlikely to be followed by immediate closure.
On Sunday, Mr Obama indicated that closing Guantanamo was a "challenge" and would take time.
"It is more difficult than I think a lot of people realise," Mr Obama told the ABC TV network.
"We're going to get it done, but part of the challenge that you have is that you have got a bunch of folks that have been detained, many of whom may be very dangerous, who have not been put on trial or have not gone through some adjudication."
These comments sparked questions as to whether Mr Obama would keep his campaign promise on Guantanamo, so his advisers are now letting it be known that he intends to act quickly, says the BBC's Jonathan Beale in Washington.
However, the Obama administration will have to work out where the remaining inmates will go and where to try those detainees the US believes have committed terrorist acts, our correspondent says.
Some of those still being held at the facility have expressed concerns about being persecuted if they are returned to their home countries.
Obama transition officials have been consulting widely with experts on the legal, human rights and military questions.
In broad terms, the idea seems to be to abandon the military tribunals authorised under the Military Commissions Act 2006, setting up a trial procedure in the US instead.
Transition officials have also been investigating ways of transferring many of the detainees to other countries.
The Bush administration set up the Guantanamo Bay camp in 2002 to hold foreign terror suspects captured during the war against the Taleban and al-Qaeda in Afghanistan.
The camp once held some 750 inmates, believed to be mostly foreigners detained in Afghanistan on suspicion of being Islamist fighters.