PARIS (Reuters) - Francois Hollande, the favorite to run for the main opposition Socialist Party in France's 2012 election, lost ground to rival candidate Martine Aubry in an opinion poll of left-wing voters ahead of a decisive primary ballot next Sunday.
In the first poll of voting plans since the two qualified on Sunday for the October 16 runoff, Hollande, a moderate left-winger, saw his predicted score slip four points to 54 percent.
His more old-school rival Aubry rose four points to 46 percent in the survey Opinionway pollsters, published on the website of the daily Le Figaro newspaper.
The figures were based on responses by all left-wing voters, tying in with the Socialist Party policy of letting anyone who pledges support for left-wing values to participate in the country's first "open-door" primary.
Socialist Party members showed broader support for Hollande, a party leader for 11 years. The poll showed 58 percent support for him versus 42 percent for Aubry, a onetime labor minister and known for her role introducing the 35-hour work week.
Hollande came in first in the first-round of the primary on Sunday, scoring 39 percent, against 31 percent for Aubry.
But the party has been rocked by a surprisingly strong showing for a more strident leftist, Arnaud Montebourg.
Montebourg, who wants the state to take partial control of banks and usher in a level of European protectionism against Chinese competition, scored 17 percent on Sunday, three times the level expected.
His victory makes Hollande's victory in round two on October 16 less certain and could pull the Socialists' campaign message further to the left.
(Reporting By Gerard Bon; Editing by Michael Roddy)