French far-right leader Marine Le Pen switched her presidential campaign back to immigration Sunday, saying all meat in Paris was halal, as she tries to head off President Nicolas Sarkozy's attempts to lure her supporters.

At a weekend congress of her National Front party in the northern city of Lille, Le Pen returned to familiar anti-immigration territory, saying she had proof that all meat in Paris was halal and that she would lodge legal complaints against distributors for misleading consumers.

This situation is a real deception and the government has been fully aware of this situation for months, Le Pen told reporters on the sidelines of the conference. All the abattoirs in the Paris region sell halal meat without exception.

The main meat industry association, Interbev, denied the allegation saying the vast majority of the meat in Paris is not slaughtered under halal or kosher practices.

While some halal and kosher meat does find its way into other distribution channels that doesn't affect the quality of the product in any way, the association's president Dominique Langlois told France Info radio.

Le Pen is third in opinion polls behind Socialist candidate Francois Hollande and Sarkozy. The first round of the presidential election is on April 22.

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Election poll graphic: http://r.reuters.com/was36s

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Exploiting discontent over globalisation and the debt crisis in Europe, Le Pen had sought to attract voters by shifting from a traditional emphasis on immigration and French identity to leaving the euro and imposing protectionist barriers.

Her stance struck a chord, especially among working class voters suffering economic hardship.

But most analysts deem her economic program as not credible and have questioned the strategy of shifting from the party's core message. Criticism of her economic policies has provided an opportunity for conservative Sarkozy to poach far-right voters as he did in 2007 when he ran on a strong security and immigration platform.

Nicolas Sarkozy is trying to renew 2007 by encroaching on our turf, Nicolas Bay, Le Pen's adviser on immigration issues, told Reuters. That means we have to go on the offensive as we have no intention of letting him do it again.

At one point in January, Le Pen was snapping at the conservative leader's heels, but a BVA poll Friday showed Sarkozy had an 11 point lead over her in the first round of the election, although Hollande would comfortably beat the incumbent in the May 6 runoff.

Announcing his campaign on February 15 Sarkozy insisted on limiting immigration and proposed a referendum on battling illegal immigration, something the far-right has been championing for several years.

IMMIGRATION POLICIES

Le Pen's National Front, founded 40 years ago by her ex-paratrooper father Jean-Marie, is still fuelled by anti-immigrant rhetoric. Among her ideas for protecting welfare are toughening citizenship requirements, shutting borders and forbidding foreigners from access to any social aid.

Bay said it was important that issues such as the halal meat claim were made public to show how Muslim values were increasingly influencing local policy and endangering France's secular tradition.

Sarkozy's government has toughened its message on immigration and in January it trumpeted the deportation of a record number of illegal migrants in 2011.

He has set himself the goal of cutting legal migration to France to 150,000 people a year, having cut the quota to 180,000 from 200,000 in past years.

Le Pen says the immigration and security policy was posturing for electoral gain and that crimes committed by foreigners had risen as the number of immigrants had risen.

The 43-year-old former lawyer says immigration costs France as much as 70 billion euros a year and has pledged to reduce the number of immigrants to 10,000 a year.

I think in 2007 (Sarkozy) managed to blind side us using our themes because he was able to appear as a new candidate ... and the National Front didn't have the dynamic we have now with Marine Le Pen, Bay said. But now his track record is bad and we have momentum around Marine so it will be difficult for him.

(Additional reporting by Gerard Bon and Patrick Vignal; Editing by Rosalind Russell)