The survey forecast Sarkozy would lead in the first round vote but still lose out to Francois Hollande in the run-off. It was a symbolic boost for the French leader who had consistently trailed Hollande for the past five months.
Sarkozy, asked about the poll, coolly noted that "it's true that it's better when things are going well", but warned that "nothing is settled, nothing is finished".
His spokeswoman claimed there was "panic" among the Socialists after the Ifop poll said Sarkozy would would win 28.5 percent of the vote in the first round on April 22, against 27 percent for Hollande.
Hollande, who has never held a ministerial post and whose ex-partner Segolene Royal lost to Sarkozy in 2007, was still on course to win the second round on May 6 with 54.5 percent against Sarkozy's 45.5 percent, the poll said.
A second survey by TNS Sofres-Sopra Group, however, showed Hollande still in the lead with 30 percent of the first round vote and Sarkozy down two points to 26 percent. It also showed Hollande winning the second round with 58 percent to 42 percent for Sarkozy.
The Socialist candidate dismissed the importance of the poll showing Sarkozy ahead and echoed his right-wing rival by saying that the electoral race was far from over.
"What counts for me is not the polls... it is the votes of the French people," he told a campaign rally in Valence in southern France.
The Ifop survey of 1,638 people was carried out by telephone, shortly after tens of thousands of Sarkozy supporters turned up in a Paris suburb on Sunday for his biggest campaign rally so far.
Sarkozy's UMP party had billed that gathering as a key part of its bid to turn the tables on Hollande.
The president, who had initially campaigned as the self-styled saviour of Europe's single currency, thrilled the cheering crowd with a surprise new eurosceptic stance.
In a tub-thumping speech, he threatened to pull France out of Europe's 26-nation passport-free travel zone unless the European Union does more to keep out illegal immigrants.
And he demanded the EU adopt measures to fight cheap imports, warning that France might otherwise pass a unilateral "Buy French" law.
The left was quick to attack what they saw as a populist stunt, with Hollande's team accusing Sarkozy of behaving like a eurosceptic British prime minister.
Marine Le Pen, the leader of the anti-immigrant, anti-EU National Front, meanwhile secured the backing of enough local government officials to run in the two-round presidential election, her party said Tuesday.
"From today, millions of citizens will regain hope... and finally be represented in the election," Le Pen said.
All French presidential candidates must have the signed endorsement of 500 elected local mayors and officials -- of which there are around 42,000 in France -- by a March 16 deadline.
Although polls consistently put Le Pen in third place in the presidential race, there was speculation that few mayors or regional councillors wanted to take the political risk of associating themselves with her campaign.
Her father Jean-Marie Le Pen has repeatedly claimed in the past that he was struggling to garner the signatures necessary to stand for the presidency, but was able to do so at every presidential election since 1988.
Philippe Poutou, a car worker who is running for president as the New Anti-Capitalist Party (NPA) candidate, has also gathered the necessary 500 signatures, his party said Tuesday.
The Ifop poll said Poutou would take 0.5 percent of the vote in the first round.