Mr Uribe is seen by many as Washington's main ally in the region
Colombian President Alvaro Uribe has left for a tour of South American nations concerned about plans to boost the US military presence in Colombia.
He travels first to Peru and will also stop in Brazil and Chile, which have expressed alarm at plans to relocate US anti-drug forces to Colombia.
Bogota relies on Washington's support in the fight against drug traffickers and left-wing rebels.
The US-Colombian deal is expected to be signed later this month.
Mr Uribe, accompanied by Colombian Foreign Minister Jaime Bermudez, will also visit Argentina, Chile, Paraguay and Uruguay.
The Colombian leader will not visit neighbouring Venezuela and Ecuador, which have protested most strongly against the planned US deployments.
During the tour, Mr Uribe's central message will be that the US presence does not threaten any other nation and that any other nation and that the war on drugs and terrorism benefit everyone, the BBC's Jeremy McDermott in Colombia says.
He says that while the final details of the document have yet to be published, it seems a 10-year agreement will be signed allowing US troops, aircraft and naval vessels access to at least four Colombian bases.
However, there is very little practical change to the US presence in Colombia, which has been a fact of life since 1999 and the launch of the US anti-narcotics strategy known as Plan Colombia, our correspondent says.
There is no change to the number of troops that can be stationed in the country: a maximum of 800 soldiers and 600 defence contractors.
Washington's main base was, until 17 July, at Manta in Ecuador but US troops were asked to leave by President Rafael Correa after the lease expired and was not renewed.
In a separate development, Washington has announced that US National Security Adviser James Jones will visit Brazil to discuss a number of issues of "mutual concern".