The three rivals hoping to be France's Socialist presidential candidate have laid out their views on foreign affairs in a final televised debate.
Ms Royal's critics say she is weak on foreign affairs
Front-runner Segolene Royal faced ex-ministers Laurent Fabius and Dominique Strauss-Kahn - both perceived to have more international experience.
The debate covered Iran's nuclear programme, Turkey's position in Europe and France's relationship with the EU.
The Socialist primary election is scheduled for 16 November.
The winning candidate is likely to face Interior Minister Nicolas Sarkozy, leader of the conservative UMP party, in the presidential election, set for 22 April.
President Jacques Chirac's five-year term expires in mid-May and he is not expected to run for a third term.
The TV debate followed the same non-confrontational format as the previous two meetings, which were criticised because all the questions were submitted in advance and there were no spontaneous exchanges.
The trio's differences were starkest on the issue of Turkey's application to join the EU.
While Mr Strauss-Kahn, a former economy minister, backed Turkey's eventual membership, Mr Fabius, a former prime minister, said it should be offered nothing more than "a privileged partnership".
Ms Royal, who had previously been vague on the issue, said there should be a "pause" in EU expansion and said she would favour a referendum of the French public - which is believed to oppose Turkish membership.
The three all said they wanted France to continue to be a key US ally, but one that would maintain its independence in policy decisions.
The debates have been criticised for being dull
However, Ms Royal criticised the Bush administration, saying: "We cannot accept the concept of preventive war nor succumb to the temptation of unilateralism."
She avoided the question of a US withdrawal from Iraq but said the international community needed to help Iraqis build democracy, adding that any success would be solely due to their effort.
On Iran, Ms Royal insisted the country should not be allowed to enrich uranium, but the others disagreed, saying that would only antagonise Tehran.
Ms Royal, who leads France's Poitou-Charentes regional council, retains a clear lead over her rivals, polls say. But she may yet be forced into a run-off contest on 23 November.