PARIS (Reuters) - Far-right candidate Marine Le Pen sought on Tuesday to turn the debate in the final week of France’s presidential election to immigration as she tried to reverse a dip in polls.

Surveys of voting intentions have for months shown Le Pen and centrist Emmanuel Macron qualifying on Sunday for the May 7 run-off. But the National Front leader has been under pressure since the start of April as conservative Francois Fillon and far-leftist Jean-Luc Melenchon closed the gap on the favorites.

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Speaking to a rally in Paris on Monday, she vowed to suspend all immigration with an immediate moratorium, shield voters from globalization and strengthen security. Those subjects won her core backing, and she hopes it can give her boost with about 30 percent of voters still undecided.

“For several weeks, we will need to assess the situation. The reality is that immigration is massive in our country and that migration flood that we are experiencing is not a fantasy,” Le Pen told RTL radio on Tuesday as she fleshed out details of the moratorium announcement.

The measure has not been part of her program, although she has put on record that she wants to limit annual immigration to just 10,000 people a year.

“I will carry out this moratorium for the exact purpose of implementing this 10,000 figure,” she said.

Until now, Le Pen has struggled to get her opponents in the presidential race to debate her party’s trademark tough security and immigration stance. She, by contrast, has been put on the defensive over her position on leaving the euro zone, a proposal that lacks wide support.

Two polls on Tuesday showed Fillon and Melenchon still a few percentage points away from Le Pen and Macron. She would be beaten by any of the three others in a run-off, polls have repeatedly shown.

Le Pen’s stance on immigration mainly competes with that of former prime minister Fillon, who despite being plagued by a financial scandal is slowly recovering in the polls, and has also targeted far-right voters.

Fillon told Europe 1 radio on Tuesday that Le Pen’s moratorium idea was nonsensical, and that while numbers should come down, the key was to impose the country’s values and identity.

“Immigration must be regulated because we have an economic, social and housing situation that doesn’t enable us to welcome as many people who want to come here,” Fillon said.

“(But) a moratorium makes no sense. What threatens us is not immigration, but the surrender of our values and our history. If we are proud of our history and defend it, then we will integrate foreigners more easily.”

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Security - which Le Pen links closely to immigration - was threatening to once again become a campaign issue on Tuesday after two men were arrested in Marseille, in southern France, on suspicion of planning an attack during the voting.

More than 230 people have died in militant Islamist attacks over the past two years, mostly at the hands of home-grown jihadists, often of north African descent.

However, with no major attacks on French soil since last summer, polls show that unemployment, stuck around 10 percent, and political integrity - an issue that has arisen after accusations of nepotism leveled at Fillon in particular since early this year - are bigger issues for voters.

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SARKOZY, JUPPE BACK FILLON

Despite his recovery, Fillon is arguably in fourth place. One of Tuesday’s four opinion polls put him on a lower score than Melenchon, as several others have done in past days and weeks. Those that pit him against the far-left showman in the second round show him losing that battle by a big margin.

Former President Nicolas Sarkozy, a divisive figure whose backing may be a mixed blessing for Fillon, on Tuesday urged voters to back the man who served under him as prime minister from 2007 to 2012, and who beat him to the party nomination in November.

“He has the experience, the desire and the project that will allow France to ensure an alternative to the last five disastrous years that we have experienced, (under Socialsit president Francois Hollande)” Sarkozy said in a video message posted on Facebook - a rare foray into the campaign by him.

Alain Juppe, also beaten by Fillon in the primaries but a more popular figure than Sarkozy, will be at Fillon’s side on the campaign trail on Wednesday, a member of Fillon’s entourage said.

Melenchon, meanwhile, was campaigning in Dijon in southeast France, with his trademark hologram image set to be transmitted to rallies in several other cities.