This week's blanket euro zone credit rating warning by Standard & Poor's has infuriated Paris and Berlin, yet it could help President Nicolas Sarkozy's re-election bid by giving new impetus to Franco-German relations.

The balance of power between France and its economically weightier partner is the topic of raging debate ahead of an April election, with opposition Socialists accusing Sarkozy of capitulating to German demands for budget control in Europe.

Sarkozy's hopes of appearing as saviour of the beleaguered euro zone seemed to stumble on Monday when he was tipped off, shortly before he and German Chancellor Angela Merkel were to present a crisis master plan, that S&P would slap a downgrade warning on most of the 17-nation currency area.

The two leaders looked strained as they outlined their proposals, yet with Germany now tainted alongside France with the possibility of a downgrade, a new solidarity was visible that belied digs by Socialists at Paris' subservience to Berlin.

It could play into Sarkozy's hands because now he and Merkel are not just in the same storm, they're in the same boat. If they start fighting now they'll only make it worse, said Philippe Moreau Defarges at the French Institute of International Relations (IFRI).

Illustrating the mood, as the S&P threat hangs over a crucial EU summit on Friday to debate the Franco-German crisis plan, French Finance Minister Francois Baroin said neither Sarkozy nor Merkel would leave the negotiating table before a deal is reached.

The best way to bring people together is to find them a common enemy. Sarkozy and Merkel now have no choice but to be more united than ever, said Moreau Defarges.

France is under much more pressure than Germany as it was the only triple-A rated euro state singled out as risking a two-notch cut. Presidential insiders have told French media Sarkozy fears the bell is tolling and that his neck is on the line.

Yet Liberation daily quoted an aide as saying: Now that Germany is under threat like us, everything is different.

Should S&P go ahead and cut France by a notch, while leaving Germany unscathed, that could tilt the balance of power back in the weeks ahead, but the sense of unity may remain.

Franco-German relations have been increasingly under the spotlight as the scramble for a solution to the debt crisis has forced Sarkozy to give ground to Berlin on the role of the European Central Bank and Brussels' power over national budgets.

For now, Paris and Berlin will have to set aside old differences over austerity and federalism to safeguard the euro.

A worsening of the crisis, with recession and rising unemployment in France, could deal a fatal blow to Sarkozy's hopes of fending off a strong challenge from Socialist Francois Hollande, who leads him in opinion polls.

Back in 2007 Sarkozy didn't believe in the Franco-German couple. Events have forced him to change. If the two countries fight he will be punished at the polls. Merkel has a piece of the French election in her hands, said Christophe Barbier, a political commentator and editor of L'Express magazine.

GERMANOPHOBIA?

Signs last week that Sarkozy might accept a loss of French sovereignty in a plan to toughen up fiscal governance prompted some Socialists to hurl abuse at the conservative government.

Hard-left Socialist Arnaud Montebourg accused Sarkozy of submitting to Merkel's Bismarck-like policies, a reference to 19th century chancellor Otto von Bismarck who unified Germany by making war on France. Another Socialist lawmaker evoked the era of Adolf Hitler.

Government officials gleefully accused the Socialists of Germanophobia and Prime Minister Francois Fillon told Hollande to put a stop to such comments.

Sarkozy struck a schoolmasterly tone as he told Merkel before journalists that he hoped Germany had not taken offence.

These remarks discredit those who voiced them. Our German friends know this is not coming from responsible people and that they should not be hurt, Sarkozy said.

He also skewered the Socialists for rejecting a balanced budget amendment to the French constitution when their German Social Democratic comrades have voted for the same measure.

What is true on one side of the Rhine is true for the other, Sarkozy said pointedly.

The Franco-German couple, key to European stability since the 1950s, hit a tense patch when Sarkozy came to power in 2007 but the global financial crisis pulled him and Merkel together and gave new momentum to the motor of EU integration.

Greece's bombshell call for referendum on a proposed new bailout, which wrecked France's hopes of a harmonious G20 summit last month, forced the duo dubbed Merkozy to act jointly to warn Athens it would have to choose whether to stay in the euro.

This time it's S&P that tried to deliver the fatal blow, but all the euro countries are concerned so there's a solidarity, said Barbier.

Despite their very different personalities, with Sarkozy's self-promoting impulsiveness sometimes grating on Merkel's matronly steadiness, the pair's body language and mutual respect suggests their arranged marriage is in a stronger phase.

In contrast, Hollande gave what most commentators called a clumsy speech this week in Berlin, criticising German ideas such as austerity and budget rules.

His lacklustre performance was a boon for Sarkozy as he tries to project the image of globetrotting world leader outshining a rival who has never served in government.

What matters at the end of the day is saving the euro zone, our relationship with Germany, restoring public finances and restarting growth, and it seems more and more like Hollande can't do that, said economist Jacques Delpla, a specialist on Franco-German cooperation.

The crisis means we need to be very close to Germany. If we disagree and are not united in fiscal discipline we are dead.

(Editing by Paul Taylor)