Mikhail Gorbachev's intensified struggle to prevent the disintegration of the Soviet Union has posed a daunting challenge to Western countries that need him to succeed but can do little to help him.

The Soviet president remains critical to many foreign policy goals of the United States. As evidenced by yesterday's talks with President Bush in Paris, his cooperation is vital for success of the international coalition against Iraq in the Persian Gulf, and will be essential later on for completion of a long-delayed strategic arms accord.

But Gorbachev, with whom the United States has conducted years of negotiations to reduce international tensions, is losing his grip on the Soviet Union, a process that the West appears impotent to change. Power is inexorably flowing from the Kremlin to the restive republics and city councils.

This devolution of power may eventually have the benefit of hastening a shift to a market economy, but for now it seems to be eroding Gorbachev's standing and threatening the very existence of the Soviet Union as a whole.

The Soviet crisis confronts policy-makers in the United States and elsewhere with a dilemma: how to encourage economic reform and the end of the command economy in the Soviet Union while not adding to the chaos and social instability that could topple Gorbachev. These goals are not easily met because Western nations have little leverage over events inside the Soviet Union.

"We want to try to help with the evolution of market systems and the evolution of the change that's taking place," Bush said yesterday. "And you want to help new friends when you find them if they're in jeopardy." The president said, for instance, that the United States would be prepared to send food to the Soviet Union "during the bleak winter" to help preserve Gorbachev's transition to a market economy and democracy.

Last week, German Chancellor Helmut Kohl made a similar gesture, and a number of European diplomats have expressed concern about the prospect of refugees fleeing mass starvation in the Soviet Union.

But American policy-makers and analysts point out that any food aid effort is complicated by the same factors that have ruined this year's bountiful Soviet harvest -- a breakdown in central control, a collapse of the distribution system and increasing political independence among the republics. One Bush administration official noted reports that there is a million tons of sugar stockpiled in Odessa, but local authorities have been unwilling to ship it elsewhere.

This official and others said they see major problems in sending food to a system that cannot handle what it already has. However, senior Bush administration aides have been examining how a food lift could be carried out if requested by Moscow to avert famine.

Ed A. Hewett of the Brookings Institution, a leading analyst of the Soviet economy, predicted that "momentum will pull Western countries into a food aid program," but he suggested it should be linked to permanent reforms in distribution and storage to avoid the mistakes of the past. Hewett said the problems run deeper than food shortages, involving a redistribution of income that is crimping the elderly and large families, as well as corrosive inflation and the widespread view that the ruble is worthless currency.

Michael Mandelbaum of the Council on Foreign Relations and the Johns Hopkins University's School of Advanced International Studies said the Bush administration may want to help Moscow but, after the recent budget battles at home, may be "terrified of giving money away" to foreigners.

"This is a time when a coordinated, large-scale Western effort ought to be discussed and it isn't being discussed," he said. "The combination of the American {budget} deficit and the gulf crisis are preventing actions we may later regret we didn't take."

While sympathetic to Moscow's plight, administration officials said they are increasingly troubled by the divergence between what Secretary of State James A. Baker III recently termed Gorbachev's "twin revolutions." In managing the external revolution in foreign and defense policy, Baker said, Gorbachev has made hard choices, "the right hard choices," leading to expanded superpower cooperation. But, he added, at home "the other and darker side of the Soviet revolution" has "unleashed age-old ethnic animosities" and failed to respond to sharp deterioration in living standards.

U.S. officials say they see no other Soviet figure with the stature and inclination to be as cooperative a partner as Gorbachev has been in superpower relations. Without Gorbachev, a senior U.S. official said, "it would be hard to see a decisive foreign policy" such as his participation in the anti-Iraq coalition and his acquiescence in the collapse of communism in Eastern Europe.

This official said the West has a difficult time judging how much power Gorbachev can give away before the country breaks up entirely. "We do feel that some further decentralization is essential to hold things together," he said. "But how much?"

Marshall I. Goldman of Harvard University's Russian Research Center said on foreign policy issues "Gorbachev is our man and it is a little scary to think what will happen if he is not there." But, Goldman noted, even Gorbachev's foreign policy ventures with the United States have become increasingly unpopular at home, with intense criticism coming not only from the military but "from the man in the street."

Goldman said there has been a rise of anti-foreign sentiment in Moscow, directed at Western businessmen. And Gorbachev's efforts to make the transition to a market economy, he said, are "beyond hope."

In response to a torrent of criticism last week that he had been too indecisive in managing the economy, Gorbachev hastily announced a plan on Saturday to radically restructure the government. He abolished the post of Prime Minister Nikolai Ryzhkov, who had symbolized the central government. He created a Federation Council, or cabinet, made up of elected leaders of the republics, the most prominent of whom is Russian Federation President Boris Yeltsin.

But many analysts and government officials said it was unclear whether Gorbachev would actually share power with the republic leaders in this arrangement, or instead, attempt to strengthen his own power in a bid to keep the country from unraveling altogether.

"My inclination is to see this as a tactical maneuver," said the U.S. official. While in theory the new arrangement would give the republics more power, Gorbachev has been "exuding the image of a centralizer" in recent weeks.

Hewett said, "They are flirting with full chaos." Not only have republics declared independence from Moscow, he said, "it is cities and regions declaring independence. This country is risking becoming a balkanized economy of well over 15 centers. In that situation you need a leader, a group of leaders . . . to bring some order to the chaos."

Gorbachev may be moving in this direction, Hewett added. "The issue is how far is he willing to go," he said. "It's just not clear because Gorbachev is going to try and minimize the power he gives to that council. His instinct is to hold onto all the levers of power he can."