THE future of the Soviet Union will be decided here in the Ukraine, amid its vast wheat fields, down in the grimy coal pits, and along the broad avenues of this capital city.On Dec. 1, the second most populous and second wealthiest republic after Russia will hold a referendum on independence and choose a president. The elections will decide whether any hope remains of a political union to replace the existing Soviet Union. As nationalist leader Vyacheslav Chernovil, one of the leading candidates for president, bluntly puts it: "A union without the Ukraine is not possible." The pro-independence mood following last month's failed Soviet coup is so strong that most observers feel a vote for independence is inevitable. But what that will mean depends more on the presidential vote. At this point, the president is likely to be one of two men: Mr. Chernovil, the radical mayor of the western Ukrainian town of Lvov and a leader of the Rukh independence movement, or Leonid Kravchuk, the former Communist Party ideology chief turned pragmatic politician who now serves as chairman of the Ukrainian parliament. As Chernovil admits, little differentiates the programs of the two men on the surface. Both envision an independent Ukraine with its own army and currency, and full control over its internal economy. While they support a nuclear-free Ukraine, the two leaders insist that nuclear weapons based here remain until their destruction through international agreement. And both acknowledge the need for some kind of transitional economic association of the former Soviet republics. But in interviews with both men this week, it is clear that Chernovil offers an uncompromising path to full independence. Mr. Kravchuk, displaying a flexibility that has served him well before, leaves the door open a crack to some form of union. "A future for the union as we saw it earlier does not exist," Kravchuk told a small group of American reporters before his departure at the end of this week to Canada, the United States, and the United Nations. But, he added, "I can envision a union of republics as an inter-republican structure.... It would mean the republics agree as independent states on the creation of some kind of unification, either a council, or a community or commonwealth." Kravchuk rejects what he calls the idea of confederation backed by Russia, Kazakhstan, and a few other republics. "We support the idea of collective security, collective defense of borders, and collective solution of a number of economic, ecological, space and other problems." Everything else, including finances, credit, taxation, economic management, and so on, is purely a Ukrainian affair, he said. Kravchuk has, however, publicly stated his support for a draft treaty of economic union drawn up by Soviet economist Gregory Yavlinsky, a document which seeks common financial, monetary, trade, and other economic policies. But in his interview on Wednesday, Kravchuk insisted he saw this as only a transitional arrangement, lasting for this year and maybe next year. He defends this on practical grounds. "Today we have no Ukrainian currency," he says. "We don't even have a chance to get credits, because ... the banks of the great powers declare that they prefer to do business with the center." Moreover, the Ukrainian economy - its energy and defense industries particularly - remains linked to the "former union." Chernovil agrees that it is not useful to break economic ties that have been established over many years. But, he told the Monitor, "The transitional economic structures are needed only for division of certain things - to divide the Army, to divide gold and currency stocks, and to divide the debt. As for other things, we need only bilateral economic ties." On military questions, the two leaders strike different tones. Kravchuk sees a Ukrainian army, but it would include forces subordinate to "the common center," though with a Ukrainian say over their use. Chernovil sees no need for a common military after the transition period. Kravchuk calls for an agreement with Russia and Kazakhstan on the future of intercontinental ballistic missiles based on the three republics' territories. Both men reject Russian President Boris Yeltsin's proposal to move the missil es to Russia. "What state hands over its nuclear weapons to another state?" Chernovil asks rhetorically. He reiterated his commitment to a nuclear-free Ukraine. "Of course, it is rather sad that Yeltsin didn't declare that Russia will be a nuclear-free zone." "I don't know whom we should fear," Chernovil grins, "the US or some of our neighbors." Beyond practical issues, the two Ukrainian politicians are divided by their pasts. Chernovil does not hesitate to point to his opponent's Communist roots. The mustachioed former journalist also trumpets his dissident past. "The ideas of anti-Communism being implemented now are the same ones for which I spent 15 years in the prison camps. I am not yesterday's or today's democrat. I've been a democrat all my life." Chernovil also criticizes Kravchuk for his hesitation during the first day of the attempted August coup, when he did not openly condemn it. Chernovil eagerly tells the contrasting tale of his own immediate moves to oppose the coup. At the Parliament that first day, he recounts, "I said to him, 'Leonid Makarovich [Kravchuk], you shouldn't think you will win by being too flexible. The putschists won't like this either. They will probably put me in jail, but you will be the next. Such barbs are not new for Kravchuk, who has long maneuvered between Rukh and more radical groups on one side and the orthodox bosses of the Ukrainian Communist Party on the other. Kravchuk's centrism is particularly important in the eastern and southern parts of the Ukraine, where the 11.5 million Russian-speaking members of the 52 million population could be the key to winning the election. Kravchuk, asked to describe his differences with Chernovil, paints himself as a realist and his opponent as an extremist. He opposes moves to carry out post-coup purges. "It's not necessary to frighten everyone with the enemy being just around the corner, to sow suspicion between the peoples of east and west [Ukraine]," he explains.