By Ingrid Melander

CHATOU, France (Reuters) - Alain Juppe kicked off his campaign to be the conservative candidate in France's presidential election on Saturday by pledging deep reforms "without exploiting fears", seeking to differentiate himself from hardline rival Nicolas Sarkozy.

Over the past week, ex-president Sarkozy grabbed the headlines in France with the launch of his primary campaign on a tough law-and-order platform including warnings that France's identity is "at threat" from immigration.

"I will never exploit fears or appeal to people's baser instincts. I want to bring hope," Juppe, an ex-prime minister, told a rally of 1,500 people outside Paris. "France, more than ever, needs to be united, because it is in a state of shock."

If elected he would be tough on crime and build more prison space but "never accept a French Guantanamo," Juppe said, referring to the U.S. prison for terrorism suspects, and to plans by some of his primary rivals to lock up all those who are under the surveillance of intelligence services.

Sarkozy, 61, and Juppe, 71, are far and away the two top candidates for the November 20 and 27 primaries that will nominate the standard-bearer of their right-wing Les Republicains party for the presidential election in April 2017.

Given the governing Socialists' deep unpopularity, the winner of the conservative primaries is very likely to make it to the second round of the presidential election and beat far-right National Front leader Marine Le Pen in that run-off to become France's next head of state.

The soft-spoken Juppe has led Sarkozy in opinion polls for months, with his more divisive opponent dogged by judicial woes and lingering voter discontent with the abrasive style that marked his 2007-2012 presidency.

Sarkozy closed some of the gap in June as Juppe's campaign lost some steam, and his ratings improved further after deadly attacks by Islamist militants in Nice and Normandy in July.


But a survey published on Saturday by Odoxa pollsters showed Juppe, who was prime minister in 1995-97, has now improved his lead.

Among those who plan to vote in the first round of the primaries, 38 percent said they would go for Juppe and 24 percent for Sarkozy, who had polled 26 percent in June. The poll was conducted throughout July and August and does not fully take account of Sarkozy's campaign launch.

Sarkozy is known as a strong campaigner and analysts warn not to rule him out, especially after the spate of Islamist attacks that have killed 236 people since January last year.

If Juppe's tone contrasted with that of Sarkozy, so did the atmosphere at their initial rallies. While Sarkozy's fiery speech roused a loud, enthusiastic crowd that cheered and applauded throughout, the calmer Juppe elicited much more subdued applause from a quieter crowd.

But his supporters said that is precisely one of the reasons they plan to vote for him, and several welcomed the fact that he did not mention the heated burkini controversy. In his first campaign rally in the south of France on Thursday, Sarkozy called for a nationwide ban on the full-body burkini swimsuit worn by some Muslim women.

"He has a dignity that other candidates don't have," 66-year-old Robert Tondre said of Juppe.

"Nicolas Sarkozy had his chance and he made many promises he did not keep," said Sarah Odoul, 28, an accountant who formerly lived in Bordeaux, where Juppe is currently the mayor, and liked what he achieved there. "I like Juppe, he works hard."

(Additional reporting by Bate Felix; editing by Mark Heinrich)