By John Irish

PARIS (Reuters) - A planned French intervention backing regional troops in Central African Republic will focus first on securing key trade routes and population hubs to stop "acts of revenge", a French defense ministry source said on Wednesday.

France is preparing to increase its force in its anarchic former colony to at least 1,000 soldiers once a United Nations resolution is passed next week to try to prevent sectarian violence from destabilizing the wider region.

The landlocked mineral-rich nation of 4.6 million people at the heart of Africa has descended into chaos since the Seleka coalition of rebels, many of them from neighboring Chad and Sudan, ousted President Francois Bozize in March.

Seleka leader Michel Djotodia, installed as an interim president, has failed to control his mostly Muslim fighters, who have preyed upon the mainly Christian population, unleashing a wave of tit-for-tat killings.

"The general plan is to have a bridging force. We are not going there to replace African forces, but to support and accompany them until they are fully operational," said the French Defense Ministry source, who declined to be identified.

"Beyond our 400 soldiers in Bangui, the reinforcement of our contingent will restore minimum security in Central Africa (CAR) on its main routes and principal population centers to stop acts of revenge and restore security so that humanitarian organizations can return and African forces can retake control."

The French-drafted U.N. resolution would give a six-month mandate for French troops and the African-led International Support Mission (MISCA) to restore order, protect civilians and rebuild state authority.

NOT LIKE MALI

The aim is for French troops in CAR to restore law and order until the 3,600-strong MISCA force is fully operational.

The African Union is due to take control next month of a 2,500-strong contingent already deployed by the Economic Community of Central African States, although the French source described that force as "not very active."

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"They are not really patrolling. We hope that our action will incite them," he said.

One of the initial objectives will be to secure the road from neighboring Cameroon to the riverside capital Bangui, allowing supply trucks into Central African Republic.

The government is currently unable to pay salaries, having lost its main financial lifeline from customs levies, and has had to rely on money from neighboring Congo Republic, although a 25 billion CFA ($50 million) loan has now run out.

"There is an urgent need for our troops to restore security. That's our priority," the French source said.

The source dismissed comparisons with Mali, where France intervened earlier this year to oust al Qaeda-linked rebels.

"There may not even be a fight here. In Mali, we faced jihadists who were fanatical and weren't scared of dying. They were equipped, trained and structured. The threat in CAR is radically different. They are groups that are not commanded, are spread out and have crude weapons.

"Seleka is already weaker than at the start of its operations. They are more like warlords and disorganized bandits than jihadist fighters," he said, and the hardest part would be identifying the several thousand fighters.

He added that France was unlikely to focus on other military objectives such as chasing down Uganda's brutal Lord's Resistance Army rebellion, which has taken advantage of the absence of state authority in eastern CAR to seek out refuge.

"They are an element that have been there for a long time. There isn't a major risk that they spread out."

(Editing by Mark Heinrich)