A key economic adviser to Soviet President Mikhail Gorbachev predicted yesterday that his "500-Day Plan" to transform the Soviet economy would win quick approval from the Soviet legislature.

Stanislav Shatalin, who is returning to Moscow today after a two-week visit to the United States that included meetings with top officials of the Bush administration, told writers and editors of The Washington Post that Gorbachev favors the plan and has been working to build a political consensus for it. He said the legislature will probably begin a week's debate on the program Monday.

The Shatalin program for turning around the rapidly deteriorating Soviet economy are considered so radical that many Soviet politicians have shied away from fully embracing it. The plan envisions putting state property in private hands, establishing a system in which prices and wages are set by market forces, not the government, and allowing complete foreign ownership of companies and property.

Despite its radical nature, Shatalin noted, the plan has been adopted fully by the Soviet Union's Russian republic, headed by Boris Yeltsin. Gorbachev is preparing his own program, which Shatalin said will be 99 percent the Shatalin program. The economist said the 500-day program has the support of all but one of the 15 Soviet republics, which have become more independent as the country throws off the economic and political shackles of 72 years of Communist rule.

The economist said the Soviet Union should evolve toward a federation of sovereign republics with a common currency, tax system, budget and monetary and credit policies. These policies, however, would no longer be set by the central government, but rather would flow upward from the republics to Moscow.

"Fundamentally," Shatalin told an earlier press conference, "the main ideas of the {economic} union have been approved by all the republics."

Although Shatalin, a member of Gorbachev's presidential advisory council and principal architect of the 500-Day Plan, has been accused by hard-line Communists of trying to dismember the Soviet Union with his decentralized economic program, he asserted yesterday that his plan is the best hope to keep the country together.

"I think the plan is the only way to save a normal Soviet Union -- not an empire and not a totalitarian state," he said.

On economic matters, he said, the Soviet republics "should try to act as one . . . because this is the only way we could more or less stabilize our economy and gradually leave the crisis behind."

Shatalin said the first priority should be the stabilization of the Soviet ruble, which has plunged in value as Soviet citizens either use foreign currency or barter to get needed goods, and its transformation within 18 months into a currency that is readily convertible around the world.

He said Moscow needs Western aid to accomplish the transformation but that technical help is more important than the credits that Gorbachev has been seeking. "Money gives you a chance to feed someone just once. But if you succeed in changing the mindset of people, changing the way they think and act, they will be self-sufficient for a long time," Shatalin said.