The group is also holding hundreds of Colombian hostages.
"The immediate release of Betancourt would be enough for us to consider the humanitarian exchange under way, in that we would conditionally suspend the sentences of guerrillas who are part of the agreement," Restrepo said on Thursday.
|"The government has joined the national and international cry that the life of Ingrid Betancourt be saved"|
Luis Carlos Restrepo, Colombia's peace commissioner
He said that the Colombian government, under President Alvaro Uribe, was not placing a limit on the number of prisoners it could release and had "reduced to a minimum" its conditions for the swap.
In return for the hostages' freedom, in turn those Farc fighters released would have to promise not to return to the ranks of the rebel group, AP reported.
"The government has joined the national and international cry that the life of Ingrid Betancourt be saved. We cannot run risks in this case and there is no more time to wait," Restrepo said.
Wolmar Perez, the Colombian human rights ombudsman, said on Thursday that the government had obtained reports that Betancourt, who was captured by the group six years ago, was in "very, very delicate" health, suffering from malnourishment and possibly hepatitis B.
The Farc reportedly took her for treatment to a first aid station in a jungle town controlled by the group in March, Perez said.
On Friday, Fabrice Delloye, Betancourt's ex-husband, praised the move as a "positive step" but called on Restrepo to be more specific about when and where the two sides would meet for negotiations.
Al Jazeera's Monica Villamizar says that Betancourt remains the Farc's biggest bargaining chip and it had been unclear whether they would be interested in letting her go and gaining nothing in return.
However if her condition has worsened and anything were to happen to her the Farc could be blamed by the world who is watching her plight closely, our correspondent adds.
Efforts to mediate a prisoner swap between the Revolutionary Armed Forces of Colombia and the Colombian government faltered after Colombia's cross-border raid on a Farc camp in Ecuador on March 1 killed one of the group's senior leaders and several other fighters.
Uribe has also rejected Farc demands that a large, populated area in the west of the country be demilitarised as the possible site of negotiations and a prisoner exchange.
|The Farc released several hostages|
earlier this year [AFP]
The group released two women hostages in January and four more Colombian ex-politicians in February, following mediation efforts by Hugo Chavez, the Colombian president.
France has urged Farc to accept the offer from Bogota.
"We call on the FARC to seize without delay this opportunity at a crucial moment," Frederic Desagneaux, foreign ministry deputy spokesman, said. "She must urgently be freed."
The Farc have been fighting a bitter four-decade civil war against the Colombian government, accusing it of oppressing the country's poor.
The government in turn accuses the group of extortion and profiting from drug-trafficking.
Thousands have been killed in the fighting.