French President Nicolas Sarkozy's supporters were shell-shocked by Sunday's vote, which gave the left a majority in the upper house for the first time in French history, and the week promised more revelations in an ongoing party-funding scandal.

He summoned key lieutenants Prime Minister Francois Fillon and UMP party leader Jean-Francois Cope to the Elysee early Monday for crisis talks, seeking a way to reconnect with voters in the seven months before the election.

"The moment of truth will come next spring. The battle begins tonight," Fillon said in a statement late Sunday after the results became known.

The opposition Socialists were delighted by the result, and their likely champion in next year's battle to unseat Sarkozy, Francois Hollande, said: "In a way it's like a premonition of what will happen in 2012."

Two of Sarkozy's ministers were elected to the Senate despite the right's broader defeat and may have to be replaced in a mini-reshuffle, and he can expect more of his closest allies to face police questioning this week.

Last week, two of Sarkozy's former aides, including a close friend who was best man at the president's 2008 wedding, were arrested and charged with taking kickbacks on a Pakistani arms deal to fund a previous election campaign.

Now, all eyes are on Sarkozy's political mentor, former prime minister Edouard Balladur, who is also expected to face questioning in the same case, according to some reports as early as Monday.

Sarkozy was spokesman for Balladur's failed 1995 presidential bid, which prosecutors now allege was partly funded by the kickbacks on a deal to sell Pakistan submarines. The president denies any role in campaign funding.

Funding scandals are common in France, but the submarine deal became toxic after claims that a 2003 bombing in Karachi that killed 11 French engineers was ordered by vengeful Pakistani agents after they missed out on bribes.

Meanwhile, Sarkozy's former interior minister and the likely head of his election campaign, Elysee aide Brice Hortefeux, may face police questioning over a telephone call he made to one of the arrested official last week.

Hortefeux called former Sarkozy adviser Thierry Gaudet to warn him that his estranged wife, Princess Helene of Yugoslavia, was spilling secrets to investigators. The call was taped by police and leaked to the press.

Sarkozy's opponents are now demanding that Hortefeux be investigated for interfering with a supposedly confidential independent judicial probe.

Eva Joly, a former anti-corruption prosecutor who will stand against Sarkozy next year as the Green Party candidate, said Balladur should be questioned and Hortefeux should "quit public life".

"If I was elected president there would be no more skeletons in the cupboard. You wouldn't see a former interior minister contacting a witness in a criminal inquiry," she declared on the BFM-TV news network.

Labour Minister Xavier Bertrand accused the left and the media of jumping on the "Karachi affair" to smear the president and comparing it to the Clearstream scandal, a previous graft case in which Sarkozy was unfairly accused.

Sunday's Senate vote, carried out by an electoral college of elected mayors and local and regional councillors, gave the left a 177-seat majority in the 348-seat upper house, previously always controlled by the right.

But the outgoing UMP speaker, Gerard Larcher, hopes to cling on to power by back-room deals with independents and dissident leftists. A vote to choose the speaker will be held on Saturday.