MOSCOW — PRESIDENT Boris Yeltsin is relying on "shock therapy" to revive the ailing Russian economy, but a mixed reaction among the population raises doubts whether the prescribed treatment will lead to a cure.The Russian Congress of People's Deputies on Thursday debated Mr. Yeltsin's radical economic reform plan, which was expected to win approval. The blueprint's main provision is the lifting of price controls, a painful but necessary step if the republic is to move to a market economy, Yeltsin said in a speech to the congress last Monday. To ensure the smooth implementation of the plan, the president also said he is ready to assume additional responsibilities as prime minister. The planned liberalization of prices prompted many Russian economists and prominent politicians to compare Yeltsin's ideas to "shock therapy" reforms underway in Poland. Given Russia's economic free-fall, many added, drastic steps were needed. "This is the only way out of the critical situation that we now find ourselves in," said Vladimir Lysenko, leader of the progressive Republican Party of Russia. But the reforms aren't without risks, especially to Yeltsin, who is placing his political career in danger by becoming prime minister and assuming full responsibility for the plan. Many called Yeltsin "courageous," but Mr. Lysenko sees no alternative. Yeltsin is by far the most popular politician in Russia, and the only way the people will go along with drastic price rises is if they believe in the leadership, he says. "The price rises will certainly bring discontent, and Yeltsin is the only one capable of preventing unrest," Lysenko says. Just how bad the situation will be this winter, nobody is willing to predict. With the lifting of controls, prices of many staple goods are expected to skyrocket. At the same time, Yeltsin is trying to prevent hyperinflation and says the government will tightly control the money supply. Though some efforts will be made to boost social protection programs, individuals will be left to manage largely on their own - a frightening prospect to many who have received cradle-to-grave security from the state for most of the last 74 years. In Moscow, a traditional bastion of support for Yeltsin, anxiety over the price hikes is palpable, but many still have faith in the Russian president. Some older Muscovites say that if they could survive World War II, they would manage during the critical days ahead. "We have the resources. All we have to do is work and we'll be fine," says pensioner Lena Ivanova, her breath foggy in the 20-degree F temperature. In other regions of Russia, however, public opinion isn't fully behind Yeltsin. In the autonomous republic of Tatarstan, 700 miles east of Moscow, many said they didn't trust Yeltsin and wouldn't rule out the possibility of protests. "From the start, Yeltsin has talked a lot and done little. His latest words are just more of the same," says Fattikh Malgazyan, an assembly line worker at the Kamaz truck plant in the Tatar city of Naberezhniye Chelny. Though Yeltsin has the backing of many progressive leaders, the support appears fragile. Some are concerned because the president's plan lacks specifics. "The machinery for liberalizing prices is absent," says economist Arkady Volsky. "Just to declare price liberalization [is not enough]." Lysenko, the Republican Party leader, says the Russian president needs a coalition of democratic leaders behind him, otherwise disaster could result. "If he is left to face the enraged masses one-on-one, the situation may end up like in Romania," Lysenko says. "Miners could come to Moscow and demand his resignation." Yeltsin has said if all goes well under his plan, the economy will begin to stabilize by next fall. But critics say the target is hopelessly unrealistic. Historian Roy Medvedev, cofounder of the Socialist Party of Workers, says the most difficult period for Russia won't start until next fall and will last two or three years. If that's the case, Mr. Medvedev's party - which calls itself the rightful heir to the disgraced and disbanded Soviet Communist Party - could quickly gain in popularity and pose a threat to the Yeltsin-led reform movement. As recent results show from parliamentary elections in Poland, in which ex-Communists did surprisingly well, the people's patience for drastic reform is short. And many political observers say Yeltsin will have less time than his Polish counterparts to produce results. The Russian "shock therapywill be much worse than in Poland because the [Russian] economy is already out of control," says economist Yevgeny Yasin. "I don't know what kind of shock there will be," Mr. Yasin continues. "I can only hope there will be some therapy at last."