* President Santos says ELN has agreed to free captives
* Guerrilla group also holding a Canadian
* Santos' popularity rating hits new low
By Luis Jaime Acosta
BOGOTA, Feb 25 (Reuters) - Colombia's government on Monday authorized a committee of civilians and Red Cross officials to travel to a jungle zone where it hopes two German hostages will be freed by the nation's second-largest guerrilla group.
The National Liberation Army (ELN) said in early February they had captured two German men in Catatumbo, near the border with Venezuela, the second time in a month it seized foreigners.
"They sent us a message saying that if we authorized the Red Cross and a committee that already exists to interact with the ELN ... they would immediately release the two German hostages," President Juan Manuel Santos said.
"I'm going to give the authorization so those German citizens are free as soon as possible. I expect the ELN to honor their word."
The ELN identified the two captives as Uwe Breuer and Gunther Otto Breuer. The rebels initially said they considered them to be intelligence agents because they could not explain why they were in the area.
The German government, however, said they were pensioners traveling in a four-wheel drive through South America.
The ELN is not engaged in talks currently underway in Cuba to bring an end to five decades of war between the government and the Revolutionary Armed Forces of Colombia, the country's largest rebel group known as FARC.
Attempts by previous governments to halt the war ended in shambles and helped energize the FARC and intensify fighting. Santos' popularity has been falling for about a year, in part because many perceive the rebels are gaining ground.
SANTOS' POPULARITY PROBLEM
A poll by Invamer Gallup released on Monday showed Santos with 44 percent of support, the lowest since he took office in August 2010, and down from 53 percent two months ago.
The poll was conducted Feb. 13-20 with 1,200 people and has a margin of error of 3 percentage points.
The 61-year-old president has not said if he plans to run for re-election in May 2014, and analysts say that may depend on the success of the peace talks.
In January, the ELN kidnapped six mine workers including a Canadian and two Peruvians in northern Colombia, as the group stepped up pressure on the government in an apparent bid to be included in peace talks with the FARC.
The ELN released five of them about a week ago, but they still hold the Canadian citizen. The hostages all worked for Canadian mining company Braeval at its Snow mine project.
The ELN has battled a dozen governments since it was founded in 1964 and is considered a terrorist group by the United States and European Union. Both the ELN and FARC have stepped up attacks on infrastructure this year and last, hitting oil pipelines and power lines repeatedly.
ELN chief Nicolas Rodriguez told Reuters last year it was willing to hold unconditional peace talks to end the war, but refused to end its kidnapping, bomb attacks and extortion of foreign oil and mining companies before negotiations start.
The group is believed to have about 3,000 fighters.