President Nicolas Sarkozy leads his Socialist challenger Francois Hollande for the first time in an opinion poll on Tuesday for round one of France's presidential election, but is still shown losing in the second round.

The Ifop/Fiducial poll put support for Sarkozy at 28.5 percent in the first round on April 22, up from 27 percent at the end of February. Support for Hollande slipped to 27 percent, from 28.5 percent, the poll showed.

Hollande would still triumph in the May 22 runoff between the two top candidates with 54.5 percent of the vote to Sarkozy's 45.5 percent, although the lead has narrowed with Hollande losing two percentage points and Sarkozy gaining two.

The election is becoming a clear two-horse race between Sarkozy, who promises tighter immigration controls, structural economic reforms and policy referendums, and Hollande, who is running on a tax-and-spend programme while also promising to cut the budget deficit.

The poll for various French media was carried out on Sunday and Monday after Sarkozy told his biggest rally yet that he would erect barriers to trade and immigration unless the European Union takes tougher stands.

Seeking to breathe new life into his campaign, Sarkozy said that Europe should have a law, modelled on the Buy American Act, requiring governments to buy European-made products.

He also threatened to pull France out of the European Union's Schengen open-borders zone unless progress is made over the year on controlling immigration flows.

Hollande said Sarkozy's move was a sign the incumbent was running out of inspiration and insisted he was focused on winning over voters and not watching every poll.

I am not going to let myself be impressed by a poll, Hollande said on France 3 TV, adding that nothing was certain yet.

On Monday Sarkozy sought to shed an image as a friend of the rich, promising a new tax on people who move abroad to avoid France's high tax on the wealthy.

Sarkozy is seeking a second term despite being one of the least popular presidents in modern France, with many voters frustrated with his poor economic record and tired of his showy style.

Separately, an Opinionway survey showed Sarkozy's approval rating slipped one point to 31 percent while his disapproval rating dropped two points to 62 percent.

It found that 50 percent of respondents thought Hollande was running the stronger campaign and 38 percent rated firebrand leftist Jean-Luc Melenchon's most highly. Only 27 percent thought Sarkozy's campaign was best.

(Reporting by Leigh Thomas; Editing by Michael Roddy)