French President Nicolas Sarkozy, 57, tried to revive his faltering re-election campaign Sunday with a mass meeting of more than 40,000 supporters at Villepinte, outside Paris. But the most important guest failed to appear.

Jean-Louis Borloo, head of the small Radical Party and a former Environment and Energy Minister under Sarkozy, shunned Sarkozy's big event, which had been supposed to demonstrate Sarkozy's ability to rally the center as well as the right to his banner.

His difficulty in winning centrist support is a crucial weakness for Sarkozy. So far in the campaign, he has tacked to the right, to fend off the challenge of the anti-immigrant National Front. He has promised to halve immigration from its current 180,000 a year and proposed that no immigrant would qualify for social welfare until they had worked and paid into the social system for at least five years. He also promised to ban halal meat, slaughtered under Muslim rules, from French schools.

In his big speech Sunday, Sarkozy threatened to withdraw France from Europe's passport-free zone unless tough new measures were installed across Europe to curb illegal immigration. He also called for more trade protection against Chinese and other exporters, proposing a "Buy European Act" modeled on the United States' "Buy American Act."

Along with his slogan "La France Forte" -- "A Strong France" -- this has won Sarkozy some support on the right, which will be important in the first round of the elections April 22. But it may jeopardize his hopes of winning crucial centrist support in the May 6 runoff round.

Another star of the Radical Party, Rama Yade, was Sarkozy's secretary of state for foreign affairs and sports minister in his first term. Of Senegalese origin and the most prominent black in French politics, she, too, ducked his big rally and voted against the lukewarm motion of support for Sarkozy that her party had reluctantly agreed Saturday.

"The 'strong France' slogan is fine but France must also be just," she said over the weekend. "We get the sense the National Front's pistol is pressed against our forehead."

The dynamics of the two rounds of voting impose a tough dilemma on Sarkozy. To be sure of getting through the first round he has to win votes from the far right. But to get elected in the second round, he has to move swiftly back to the center.

Sarkozy has a further problem; the center is already occupied. Former Education Minister Francois Bayrou leads the small MoDem (Democratic movement) and the latest polls show him rising to level pegging with the National Front at 15 percent in the first round against Sarkozy's 23 percent.

Francois Hollande, the front-running Socialist Party candidate, has 29 percent of current voting intentions for the first round. But in the second round, which is likely to see Sarkozy facing the Socialist, Hollande has a comfortable lead of 56-44 over Sarkozy.

Time is running out for Sarkozy. After Friday, French media must by law give equal time to all official candidates, even Nathalie Arthaud from the tiny Trotskyist party with less than 1 percent of the polling.

So the French president has just a few days to dominate the airwaves, stamp his agenda on the campaign and turn around those unhelpful opinion polls.

Some of the members of Sarkozy's Union for a Popular Movement ruling party in the National Assembly, particularly those who were elected with small majorities, are talking of a nightmare scenario in which Sarkozy's defeat seems so likely that there is a last-minute flood of support to the centrist Bayrou in the hope that he can stop a Socialist victory.

Among those hoping that Sarkozy can yet win through are German Chancellor Angela Merkel, who has campaigned for him, and British Prime Minister David Cameron, who says he backs Sarkozy but fears that campaigning for him could be counterproductive.

A victory for Hollande, the owlish intellectual who rose through the Socialist Party machine and has never served as a government minister, could have important implications for the European Union and for the embattled euro currency. Global financial markets are unlikely to welcome Hollande's program, which threatens to divide Europe and undermine rescue plans for the euro.

Hollande rejects the Merkel strategy of austerity and budget cuts and promises a new strategy of public investment, jobs and growth. He has promised to undo Sarkozy's reform of the retirement age, which was raised from 60 to 62, and plans a special "millionaire's tax" with a top rate of 75 percent. His program calls for the creation of create 60,000 teaching jobs and 150,000 state-funded jobs for first-time workers.

Hollande's plan to bash the rich has already inspired reports of wealthy French families decamping for the friendlier tax regimes of Switzerland, Belgium and Britain, where more than 300,000 French citizens now work in the city they call Paris-sur-Thames. Sarkozy launched his 2007 campaign in the British capital and Hollande, who speaks little English, campaigned there last week.

Sarkozy's biggest problem is his own personality and the way the campaign is becoming a referendum on him rather than on policies. While many respect him, few French voters like the mercurial French president with a notoriously short fuse. His early flirtation with the rich won him the nickname "President Bling-Bling." Earlier this month he had to take refuge in a bar in Bayonne for more than an hour as riot police cleared away a crowd of angry voters who had hurled eggs at him and threatened to beat him.

Now some advisers are proposing a new slogan for Sarkozy - "Either me or chaos."

"France will realize that the president is the only person with the energy, commitment and courage to solve France's problems and Europe's problems," says Sarkozy campaign spokesman Frank Riester. "I'm convinced of that."