President Mikhail Gorbachev is gambling that Sunday's unprecedented referendum on preserving the USSR will give him a mandate to hold together the crumbling Soviet empire.

The results, however, are not likely to be conclusive, and the referendum may well backfire and hasten the disintegration he is trying desperately to prevent.For the first time in the 74-year history of the Soviet Union, citizens are being asked to participate in a nationwide referendum, and the question could not be more important: Should the union be preserved?

Gorbachev has thrown his full weight behind getting a resounding "yes," and in the past two weeks Soviets have been subjected to the most intense and one-sided propaganda campaign since he took power six years ago. Pollsters predict he will win about 60 percent of the votes; six of the 15 republics are not participating.

The sound and fury revolve around an obtuse and ambiguous question that asks: "Do you think it necessary to preserve the Union of Soviet Socialist Republics as a renewed federation of equal sovereign republics, in which the rights and freedoms of an individual of any nationality will be fully guaranteed?"

The firestorm of Kremlin propaganda would have people believe that a "yes" vote means continuing centuries of Russian and Soviet greatness and that a "no" vote means an immediate slide into chaos and civil war.

A commentator for the official news agency, Tass, went so far as to say the future of the entire world "depends to a considerable degree" on the outcome.

That's nonsense, say many Soviets and Western diplomats. The leaders of independence-minded republics Lithuania, Latvia, Estonia, Georgia, Armenia and Moldavia have refused to participate, they note, although there may be isolated balloting there.

A senior Western diplomat said the fuzziness of the question would render the referendum almost meaningless. The progressive weekly Moscow News recently wrote that the referendum was likely to lead to greater bitterness and confrontation as both the Kremlin and breakaway republics use the results to harden their positions.

And as Gorbachev's chief rival, Boris N. Yeltsin, pointed out Friday, what are people actually voting for? What, for example, does a "renewed federation of equal sovereign republics" mean?

"To what extent will it be `renewed'?" Yeltsin, the chairman of Russia's parliament, asked in a speech. "Is it just that the facade will be repainted, or will substantial changes be made?

"The referendum is being held to get support for the present policy of the country's leadership. This policy is aimed at preserving the imperial union, the existing system, and it allows only superficial renovation."

Many pollsters and politicians are predicting that overall, in the nine republics participating in the referendum, about two-thirds of the registered voters will turn out and that roughly 60 percent will vote "yes."

If a republic votes against preserving the union, to break away it then would be required to abide by an arduous secession law. Among other things, the law would require that two-thirds of all adults in the republic approve secession in a second referendum.

If Gorbachev and the Communist Party do not get a resounding win, it will not be for lack of trying. During the past few weeks, Gorbachev and the party he heads have conducted a propaganda blitz reminiscent of the "stagnation" period of the late Soviet leader Leonid Brezhnev.

On central TV, farmers, workers and intellectuals have appeared in an unending stream on the nightly news program "Vremya." As if reading from the same script, they all have solemnly announced that they are "for the union."