Nicolas Sarkozy scored 31.1% of the vote and Segolene Royal, potentially France's first woman president, 25.8%, according to preliminary official reports. The run-off has been slated for May 6.
Centrist Francois Bayrou gained 18.5% and far-right Jean-Marie Le Pen 10.5% of the vote.
The Interior Ministry put the turnout at 85%, a level similar to the 1965 elections, when the French elected their president for the first time via a direct poll.
Experts explained the high voting numbers by the importance of the election for France, which has been rocked by student protests and youth riots in immigrant suburbs against job discrimination in recent years.
The main rivals - both post-war generation politicians - have pledged to cut government costs and preside over radical changes, with former Interior Minister Sarkozy highlighting economic reform and public order and Royal focusing on welfare and a fairer society.
Several outsiders in the presidential race have already voiced their support for Royal. The Communist Party leader, Marie-George Buffet, appealed to her voters to support Royal May 6. Another leftist leader, Arlette Laguiller, Green Party leader Dominique Voynet, and the anti-globalist far left candidate Jose Bove have followed the suit.
None of them have so far voiced support for Sarkozy. Le Pen has said he will announce his preference May 1. Bayrou is expected to choose among the favorites after party debates, his centrist party member said.
But opinion surveys indicate the ruling party's candidate is likely to win. Ipsos opinion center said 54% of voters would support Sarkozy May 6, while Royal will gain 46% of the vote.
