BOGOTA, Colombia, March 28 (Reuters) - Colombia said on Monday it was moving toward peace talks with the Andean country's second largest rebel group and called for international support.

The 5,000-strong National Liberation Army, known by its Spanish initials ELN, at the same time asked for the help of Brazil, Venezuela and Spain in ending the group's 40-year war against the state.

Since June of last year, the ELN and the government of President Alvaro Uribe have been in contact. Mexico acted as an intermediary.

"We are studying initiatives aimed at assessing the success of this exploratory phase and moving toward a peace process," Colombian Peace Commissioner Luis Carlos Restrepo said. It was a rare statement of optimism that peace with the country's Marxist guerrilla's might be possible.

"The government and the ELN highlight the effective assistance of Mexico and call for international assistance once this new drive for national peace comes to fruition," said Restrepo's statement.

The ELN meanwhile sent a letter to the left-leaning presidents of Brazil, Venezuela and Spain to help the country reach peace and create "a hopeful democracy that will make social justice possible."

The three presidents will meet with Uribe for a summit on trade and terrorism in Venezuela on Tuesday.

A peace deal will not be easy. The ELN wants Uribe to free ELN prisoners held in Colombian jails and negotiate a bilateral cease-fire. Uribe has said the ELN, which funds itself by kidnapping, must unilaterally disarm if talks are to take place.

While Colombia's biggest guerrilla force, the Revolutionary Armed Forces of Colombia, or FARC, and right-wing paramilitary militias have grown rich on the country's huge cocaine business, the ELN has sworn off drug smuggling.

This leaves it at a financial disadvantage that may help prompt it to follow the steps of former rebel group M-19, which in 1989 negotiated a deal to disarm.

Uribe, an ally of Washington, criticized the previous government's failed effort at negotiating with the FARC.

But peace with the ELN may help Uribe clinch international backing for his effort at demobilizing Colombia's paramilitary groups. Critics have said Uribe's approach does not take into account the complexity of Colombia's criminal organizations.