* African structure of force would remain, says Fabius
* U.N. peacekeeping force has financial advantage
* Role of French troops would need to be defined (Adds background, quotes, French UN envoy)
By John Irish
PARIS, Feb 6 (Reuters) - France wants the African-led military mission in Mali to be replaced with a United Nations peacekeeping mandate by April, Foreign Minister Laurent Fabius said on Wednesday.
Having swiftly seized the main towns in northern Mali from Islamist militias in a three-week campaign, France is keen not to get bogged down in a costly long-term deployment.
"From the moment that security is assured, we can envisage without changing the structures that it can be placed under the framework of U.N. peacekeeping operations," Fabius told reporters.
Asked if the aim was to have this done by April, he said: "Yes. Our experts and those we are working with are aiming for that."
According to diplomats at the United Nations, the Security Council is looking at adopting a resolution at the end of February or early March to replace the current African mission under the United Nations.
It would then take 45-60 days to "re-hat" them as U.N. forces, which would involve a reduction of their number, the diplomats said.
"On the one hand its an advantage because it's under the United Nations and the financing of the United Nations, but that doesn't mean that there is a modification of the organisation, but just that it will be under the umbrella of the U.N," Fabius said.
France has deployed nearly 4,000 ground troops, as well as warplanes and armoured vehicles in its three-week-old Operation Serval that has broken the Islamist militants' 10-month grip on northern towns.
It is now due to gradually hand over to a U.N.-backed African force of some 8,000 troops, known as AFISMA, of which around 3,800 have already been deployed.
French Ambassador Gerard Araud said he had raised the prospect of a U.N. peacekeeping force for Mali in the U.N. Security Council on Wednesday.
"I think that we have to wait several weeks before assessing the security environment and taking the decision of deploying a peacekeeping operation," he told reporters.
"We will have to have to have a transition from the French and AFISMA to a U.N. peacekeeping operation."
French sources said the exact role of French troops in Mali under a U.N. mandate would have to be defined.
Fabius said on Tuesday Paris would begin reducing troop numbers in Mali from March and focus its operations on flushing out Islamist rebels in the north of the country.
"That doesn't mean we're leaving. We could reduce numbers and focus in particular on searching for terrorists," he said on Wednesday. (Additional reporting by Michelle Nichols at the United Nations; Editing by Jon Hemming)