President Nicolas Sarkozy's decision to take France back into NATO's command structure despite domestic opposition is a gamble designed to help French ambitions to build a European defence identity.

Sarkozy is expected to announce at a summit of the North Atlantic Treaty Organisation in April that France will fully rejoin the alliance, reversing Charles de Gaulle's decision in 1966 to walk out in protest at US domination.

On the domestic front, French officials are casting the NATO return as a strategic coup that will cement Paris's position within the alliance and remove hurdles to building up Europe's own defence capability.

But the move is proving a harder political sell than expected, with opposition leaders accusing Sarkozy of surrendering a chunk of French sovereignty with no firm benefits for Paris nor for Europe.

France's main opposition Socialist Party warned that returning "without conditions or tangible benefits," would be fatal for plans, long championed by France, to build up an independent European military capacity.

Centrist politician Francois Bayrou called on Sunday for a referendum on the issue, warning that a "one-way ticket" back into NATO would be "a defeat for France and for Europe."

Bruno Tertrais, of the French Foundation for Strategic Research, admitted that Sarkozy was adopting a risky strategy.

"Returning to NATO is something of a gamble: the idea is that it should speed up the construction of a European defence identity, in parallel with the renewal of the Atlantic Alliance."

"The return should put a final stop to the nagging suspicion among some of our partners, who often thought we wanted to develop European defence in order to compete with NATO," he said.

Jean-Pierre Maulny, of the Strategic Institute of International Relations, agreed that Sarkozy's move was a "way of giving assurances to our European partners."

Addressing a security conference in Munich at the weekend, Sarkozy stressed again that "Europe's defence identity was a strategic and military priority," and attacked the "ridiculous" notion that France could seek to undermine NATO.

Within NATO itself, Washington has agreed to give French generals command of two structures -- NATO's Allied Command Transformation in Norfolk, Virginia, and a regional command headquarters in Lisbon -- if Paris reintegrates.

But, while the Norfolk post would give France influence over NATO's strategic doctrine, critics point out that it carries no operational clout.

Both Tertrais and Maulny said the command posts would bring few benefits for France, which is already an important participant in NATO missions despite its hands-off role in the command hierachy.

"France will not pack a bigger punch on the world stage as a full member of NATO," said Tertrais.

"But it will carry more weight inside NATO itself, and it will have a louder voice within the European Union when it comes to promoting a European defence and security identity."

Sarkozy's government has launched a major public relations offensive to secure backing for the NATO move, starting with an joint op-ed published last week with German Chancellor Angela Merkel.

Both leaders called for NATO to reinforce its strategic partnership with the European Union, as they announced that a German battalion would be stationed in eastern France for the first time since World War II.

Meanwhile NATO Secretary General Jaap de Hoop Scheffer is to address the French parliament's foreign affairs and defence committee on Thursday, followed by France's defence and foreign ministers at the end of the month.