France has been very interested in Colombia's hostage crisis since Betancourt was kidnapped while campaigning for the Colombian presidency in 2002.
Earlier this week Colombia said it wanted Sarkozy to become involved in helping resolve the impasse in talks to swap some 45 hostages, including Betancourt and three Americans, for some 500 Farc prisoners held by Colombian authorities.
Sarkozy said in his televised message: "For my part, I pledge to remain personally involved in the search for a humanitarian solution, for the liberation of all the others being held. Moreover, I promise to redouble efforts, if that is desired, to contribute to finding a way out of the Colombian conflict.
"But at this moment, Mr Marulanda, a woman in danger of dying must be saved. I have a dream: to see Ingrid among her family this Christmas.
"Mr Manuel Marulanda, you can make this dream come true, you can save this woman, you can show the world that Farc understands human imperatives.
"Mr Marulanda you bear a heavy responsibility. I urge you to assume it."
Last week, the Colombian government released excerpts from rebel videos of the hostages, sparking a public outcry over their plight.
One clip showed Betancourt gaunt and despondent at a rebel hideout.
Sarkozy's statement came after Luis Carlos Restrepo, Colombia's peace commissioner, proposed direct talks with the rebels on Tuesday.
"I am willing to go wherever the Farc wants," he said.
|Restrepo said Farc had yet to provide a list of|
names of men they wanted released [EPA]
"We are responding to national and international clamour and it is time for this drama to end ... this is a priority."