MOSCOW, OCT. 18 -- The loudspeakers in Red Square blared out "h-o-o-r-a-h, h-o-o-r-a-h" as Russia's latest would-be savior circled the Kremlin followed by hordes of admirers and television crews.

Wearing two-tone designer sunglasses and a spotless white jogging outfit, Jane Fonda today embarked on the awesome challenge of persuading 280 million Soviet citizens to get into shape. Her gentle jog around the Kremlin walls triggered what will be a veritable media blitz over the coming weeks -- complete with television shows, books, and taped workout sessions.

"Greet Jane Fonda, one of the most beautiful women in the world. She will show us a new way to live," bellowed the public address system, using the hectoring, uplifting tone familiar to Soviet citizens from May Day parades and speeches hailing the Soviet Union's glorious Communist future. "Hoorah, hoorah."

Fonda's appearance at the hub of Soviet power brought to mind, paradoxically, economists. Specifically, the parade of Soviet economists who have been offering Fonda-like cure-alls for the Soviet economy to a cynical Soviet public. In this sense, her appearance highlighted the psychological and cultural gulf that still separates Americans and Russians, despite all the talk about superpower cooperation.

Americans have a can-do, utilitarian approach to life -- typified by 30-day self-improvement programs favored by people like Fonda -- that contrasts with the philosophical, almost mystical attitudes displayed by many Russians.

The difference in national outlook may help explain some of the confusion that exists in the United States about Soviet plans for economic reform. When Soviet economists came up with a snazzily titled 500-day program to create the foundations of a market economy, Americans sat up and took notice. The assumption seemed to be that, if thinner thighs can be achieved in 30 days, then 500 days for the dismantling of communism and its replacement by capitalism is a reasonable enough target.

The typical reaction inside the Soviet Union to the 500-day plan when it first hit the headlines last summer was very different. After an initial burst of optimism, most people sank back into a deep cynicism. Ask the average Muscovite standing in line for food what he thinks of the market economy and the stock answer is: (a) it will never happen, and (b) even if it does happen, nothing good will come out of it.

There is nothing quite so shocking for first-time American visitors to the Soviet Union as the pessimism of ordinary Russians about their country's future. Americans arrive in Moscow expecting to find Russians reveling in their new Western-style freedom and brimming over with excitement about President Mikhail Gorbachev's restructuring program, called perestroika. It is disillusioning to discover a nation whose main concern is finding enough to eat.

While Fonda was jogging around the Kremlin walls in the late autumn sunshine, Soviet politicians were busy inside the Kremlin watering down the famous 500-day plan, to the dismay of its original authors.

During this morning's debate one economic expert after another got up to explain why the original 500-day plan would not work. Freeing prices would lead to hyper-inflation. Cutting subsidies to money-losing factories and collective farms would mean mass unemployment. Russians are not yet ready for radical privatization.

The creation of a market economy, responsive to the classic capitalist forces of supply and demand, remains the ultimate goal of Kremlin policy-makers. In the short term, however, Gorbachev's advisers seem to see no alternative to the old system of centralized distribution. To avoid economic chaos this winter, local authorities are now being advised to introduce what amounts to a rationing system of essential commodities.

As the economic debate grinds on endlessly, a kind of revolving door operates to fill the post of Gorbachev's economics guru. It seems as if every prominent Soviet economist has now had his 15 minutes of fame -- when his theory of how to save the Soviet Union's ramshackle economy was the one in vogue.

When Gorbachev got serious about economic reform back in 1987, he turned for advice to Abel Aganbegyan, a rotund Armenian exiled to Siberia during the bad old "stagnation" days. Aganbegyan came up with the slogan of "cost accounting," a device intended to force Soviet factory managers to start thinking about profit and loss, instead of subordinating everything to fulfilling the plan laid down by Moscow.

For a few months, "cost accounting" was on everybody's lips, repeated reverently like a mantra that would solve the Soviet Union's economic problems. But then, suddenly, it faded away as quickly as it appeared. It turned out that there was little point allowing managers to make their own investment decisions if prices were controled by the state and were therefore artificial. The old system of central planning was replaced by a new system of compulsory state orders.

Aganbegyan was exiled to the American lecture circuit, the humane, modern-day equivalent of a spell in Siberia. His replacement as Gorbachev's favorite economist was Leonid Abalkin, whose gloomy countenance suited the bleak economic outlook. Appointed first deputy prime minister a year ago, Abalkin favored a "moderate-radical" path to a "regulated market." His critics accused him of wanting to get a "little bit pregnant."

During the 12 months Abalkin has been responsible for the Soviet economy, virtually everything worth buying has disappeared from the stores. Production has begun to fall sharply. The goal of a unified Soviet market seems further away than ever. To protect their own citizens, republics, regions, even towns began declaring their economic independence from the rest of the country.

Last summer, a new star arose in the Soviet economics firmament: Stanislav Shatalin. Wry, impish, and somewhat ill-coordinated, he could play Laurel to Aganbegyan's Hardy. A self-described social democrat, despite his membership of the Soviet Communist party, he devised a simple solution to the deepening economic crisis: the biggest bankruptcy sale in world history.

After three months of hesitation, Gorbachev now seems to have concluded that the 500-day plan, also known as the Shatalin plan, is too risky. He is unwilling to sacrifice his prime minister, Nikolai Ryzhkov, who favors a more cautious approach to economic reform. So, he has given the revolving door another push, propelling into the limelight -- guess who? -- Abel Aganbegyan.

Under Gorbachev's direction, Aganbegyan rewrote the 500-day plan to remove most of its teeth. It has now, in the words of a rival economist, become a 730-day plan that is starting 50 days too late. It also has gotten off to a bad start, denounced as unworkable by the Soviet Union's two largest republics, Russia and the Ukraine.

Like his predecessors -- Shatalin, Abalkin, and Aganbegyan I -- Aganbegyan II claims that his latest plan is economically sound. Whether it will ever be put into practice is another matter. "That is a matter for the politicians. I am just an economist," he said with a grin, diving back into the Supreme Soviet chamber, where Gorbachev's compromise plan won committee approval today.