PARIS -- While the American presidential campaign gathers velocity, rushing past in a cacophonous blur, France's campaign for the presidency is creeping softly along. In the kind of literary analogy the French love, the campaign here resembles a well crafted but slowly paced murder mystery, complete with multiple misleading clues and a solution that will be revealed only on the last page.

Ideological differences in France (of all places) have dwindled to such an extent that the quick and deadly campaign ending that is being shaped here could well turn into one big throw of the dice in the form of a single televised debate, with the winner also taking the race for the Elysee Palace.

The principal author of this unfolding mystery is President Francois Mitterrand, who is still refusing to reveal if he will run for a second seven-year term in an election now only nine weeks away. The election begins with a winnowing first ballot among eight declared candidates on April 24 and almost certainly goes to a runoff between the two top vote gatherers on May 8.

The polls here continue to suggest that the old president will become the new president, with a short campaign supposedly benefiting the rose-gardening Socialist leader more than it does his two chief rivals, conservatives Jacques Chirac and Raymond Barre. These polls also show Chirac, the current prime minister, for the first time edging out Barre in the first round.

But a lengthy conversation here with Barre this week suggests that the former prime minister has an antidote in mind for Chirac's current surge and a surprise ending for Mitterrand's mystery. To the ideologically unanswerable question of how he and Chirac differ, Barre is ready to reply: I can beat Mitterrand.

As Barre will be subtly reminding conservative voters in the weeks to come, he is the only French political leader who has ever cleanly beaten the nimble Mitterrand in a televised debate. It happened in 1977, when Barre was prime minister and Mitterrand was leader of the Socialist Party. An economist by profession, Barre easily flummoxed Mitterrand on economic questions that night.

French campaign debates, unlike the ersatz press conferences billed as campaign debates in the United States, are true intellectual jousts and one of the candidates is usually left lying on the floor bleeding profusely. The closeness of this year's race suggests the TV encounter could be decisive.

Mitterrand could presumably refuse the runoff debate, the only such head-to-head event of the entire campaign. But it would be neither in his interest nor in his nature to do so. The likely date would be one of the first days of May.

Thus Barre's unspoken strategy is to begin running against the invisible Mitterrand now and ignore the omnipresent Chirac, who has already started campaigning in high gear. The two-point lead Chirac has opened up over Barre in recent polls has triggered premature press obituaries for Barre, but these ignore that those same polls show Mitterrand easily beating Chirac in the runoff, while barely edging Barre.

Barre shows no concern over Chirac's surge. He appears to be pacing himself carefully to retain the serene and composed air he now manifests throughout the campaign, despite his opponents' hopes and expectations that he will tire and revert to the professorial and scolding appearance that saddled him with high negative ratings when he left office in 1981.

Barre gives the impression of having conceptualized each minute of this campaign. He speaks of its duree, or longness, in the same way that historian Fernand Braudel writes of la duree of centuries. Once Mitterrand joins the battle, which Barre expects around March 15, Barre plans to "rise slowly" while Chirac wears out his credibility with a constant outpouring of cheery claims and promises.

Barre's stock mounts when voters are preoccupied with the economy. "Things seem not to be going too badly at the moment," he told me, thanks in part of an election-year expansion induced by Chirac's team. But "you cannot go around repeating each day that France has been saved again, that everything is wonderful anew. That rhythm is not realistic" for France.

His own message for the conservative voters is more direct: "Mr. Mitterrand does not want to see me in the second round. He is counting on Mr. Chirac to do his work for him. I have a different idea."