Mr Sarkozy effectively accused his left-wing rivals yesterday of orchestrating what he described as a "despicable forgery".
Amid mutual smear claims, Mr Sarkozy and Francois Hollande held giant rallies in Toulouse and Paris ahead of a crunch two-and-a-half-hour televised debate on Wednesday.
More than 20 million French people are expected to tune in for the lone duel ahead of the May 6 run-off.
On Saturday, the investigative news website 'Mediapart' published what it said was a copy of a Libyan regime document proving that Mr Sarkozy and Gaddafi had an illegal arrangement to help propel Mr Sarkozy to power in 2007.
Signed by Moussa Koussa, Gaddafi's intelligence chief in 2006, it refers to an "agreement in principle to support the campaign for the candidate for the presidential elections, Nicolas Sarkozy, for a sum equivalent to €50m".
But the memo's supposed recipient -- Bashir Saleh, Gaddafi's former chief of staff -- yesterday denied receiving such a document.
A lawyer for Mr Saleh, currently in exile in France, said he expressed his "grave reservations" over its authenticity.
"It's despicable. It's a forgery," an angry Mr Sarkozy insisted. "Mediapart is a habitual liar. It's a shady agency in the service of the Left.
The Socialists, nevertheless, called for a judicial investigation, saying: "Nicolas Sarkozy must explain himself before the French people."
Julien Dray, a socialist member of the National Assembly, invited Mr Hollande's campaign director, Pierre Moscovici, and other top team members to a birthday drinks party.
Little did they know that Mr Strauss-Kahn was also invited to the event at a popular disco bar on the Rue St Denis in Paris, notorious for its sex clubs.
Cleared of rape charges in the US, Mr Strauss-Kahn is under investigation in France for "aggravated pimping".
The campaign team beat a hasty retreat when warned, at the last minute, that he was on the guest list, leading Mr Hollande to make a public declaration to quash controversy.
"(Mr Strauss-Kahn) no longer has a role in political life and thus should not be part of a campaign nor in any images that could potentially lead people to believe he's coming back," he said.
The Sarkozy camp made hay of the near miss. "You couldn't make it up," said Nathalie Kosciusko-Morizet, Mr Sarkozy's spokesperson.
She said that Mr Hollande "must have known" about his former party colleague's allegedly illicit sexual practices.
Mr Hollande's aides denounced that claim as "outrageous exploitation" of the case. (© Daily Telegraph, London)