Far-right leader Marine Le Pen, meanwhile, saw her third-place position behind Hollande and Sarkozy boosted, according to the survey of 966 adults carried out by LH2 in partnership with Yahoo! Friday and Saturday and published on Sunday.

Standard & Poor's cut its rating on French debt by one notch to AA+ Friday in a blow to Sarkozy, who had previously made keeping the top-grade AAA a priority.

The number of those surveyed saying they would vote for Sarkozy if the first round of the two-round presidential elections were held next Sunday fell to 23.5 percent from 26 percent a month ago, the poll showed.

"The person who made keeping the top financial rating an 'obligation' today finds himself weakened among the electorate," the conclusions of the poll read, adding that Sarkozy would have to convince people of the relevance of his economic plans in a particularly difficult context.

Hollande, whilst remaining well ahead of the incumbent president, also saw his share of the vote slip to 30 percent from 31.5 percent, indicating that the intensification of his campaign had not convinced public opinion, according to LH2 and Yahoo!

Le Pen, meanwhile, gained 3.5 percentage points to 17 percent, extending her lead over fourth-placed centrist candidate Francois Bayrou, at 14 percent.

Hardline Left Party candidate Jean-Luc Melenchon also picked up 2 percentage points, with 8.5 percent of planned votes, according to the poll.

In a second round pitting Hollande and Sarkozy against each other, the poll showed that Hollande remained well ahead of Sarkozy, with 57 percent of the vote versus 43 percent for the current president.

(Reporting by James Regan; Editing by Alison Williams)