SOVIET President Mikhail Gorbachev appears determined to cling to power and is probing to find a place in the structure of the new Commonwealth of Independent States.The commonwealth's final shape and structures remain undefined, but it moved a step closer to becoming reality when the four Central Asian republics and Kazakhstan announced their desire to join. But at the same time, cracks already have appeared in the united facade of the three Slavic republics - Russia, the Ukraine, and Byelorussia. The leaders of the three republics unveiled the commonwealth plan Dec. 8 after meeting near the Byelorussian city of Brest. The commonwealth, as it is envisaged now, would eliminate virtually all central power structures, leaving Mr. Gorbachev without a job. Many observers expect it is only a matter of time before the president resigns. Gorbachev himself is sending mixed signals. At first he opposed the treaty, but when he found little support for his position, he said he would resign rather than accept a purely ceremonial post in the new commonwealth. Later a presidential spokesman said Gorbachev would remain in office at least until today's scheduled visit by United States Secretary of State James Baker III. Despite the speculation about the impending resignation, Gorbachev continues to lobby for some way to accommodate the sovereignty-minded republics, while retaining some sort of centralized power. Gorbachev indicated he wasn't about to step down soon, saying he was determined to prevent chaos. ll use my powers as president, first of all as commander in chief," Gorbachev said in an interview with Time magazine, to be published today. Gorbachev received support from longtime allies Foreign Minister Eduard Shevardnadze and presidential aide Alexander Yakovlev. Mr. Shevardnadze said Gorbachev would not resign "today or tomorrow," adding that he was advising him not to make a hasty decision. "The problems that we face are so acute that both Gorbachev and the presidents who started this process are needed," Shevardnadze said Saturday at the congress of the Movement for Democratic Reform. Mr. Yakovlev described the commonwealth concept at the congress as "an initiative" and suggested it could be merged with the latest draft of Gorbachev's union treaty. Russian President Boris Yeltsin has rejected that idea. The desire of the Central Asian republics - Kirghizia, Tadzhikistan, Turkmenia, and Uzbekistan - to join the new commonwealth, along with Kazakhstan, probably buried Gorbachev's hopes for a revamped union. But it also apparently put pressure on the Slavic republics, particularly the Ukraine, viewed by many to be the key to the commonwealth. The Slavic republics insist commonwealth membership is open to any former Soviet republic. But friction between the Slavs and the Central Asians was evident in a statement issued by the five Central Asian presidents, who met late last week in the Turkmen capital of Ashkhabad. "All states forming the commonwealth should be recognized as cofounders," said a communique issued by the five presidents. "The documents, decisions, and agreements should reflect the historic, social, and economic realities of the Central Asian republics and Kazakhstan, which unfortunately weren't taken into consideration during the preparation of this agreement." A meeting between Mr. Yeltsin and the Central Asian leaders over the weekend, was postponed without explanation. Splits also are appearing in the positions of Russia and Ukraine, especially regarding the military. Ukrainian President Leonid Kravchuk late last week issued a decree naming himself commander in chief of all military forces on the republic's territory. The Ukraine also said it was taking control of most nonnuclear Soviet forces stationed in the republic, including about 1.2 million soldiers. The move had the blessing of both Yeltsin and Soviet Defense Minister Yevgeny Shaposhnikov, insisted Ukrainian Defense Minister Konstantin Morozov. Mr. Morozov said the Ukraine seeks to control all Soviet armed forces on its territory with the exception of "strategic forces," including long-range missiles and bombers, as well as part of the Black Sea fleet. But that would contradict Yeltsin's definition of a united military that he gave during a meeting with top generals in Moscow last week. The Russian leader wants "strategic defense forces; rocket forces, the Air Force, the Navy antiballistic missile defense, as well as anti-aircraft defense to re main undivided," the Komsomolskaya Pravda newspaper reported. Some political leaders already are expressing doubts about the commonwealth's ability to handle the economic and political crisis. Russian Vice President Alexander Rutskoi said a big source of tension was that each of the Slavic republics interpreted the commonwealth agreement differently. He also denounced price liberalization, scheduled for Jan. 2, saying no one in the Russian government had the experience to implement it properly. Shevardnadze, meanwhile, expressed concern about the commonwealth's ability to preserve the ruble as its currency. Kiev's intention to issue its own currency was the chief reason Yeltsin sought to create a commonwealth with the Ukraine and Byelorussia. "They talk about a common currency system, but I don't think they'll create this without any problems," Shevardnadze said. With new power structures still ill defined, the foreign minister repeated warnings about the possibility of another coup attempt, adding control over the Soviet nuclear arsenal was one of his biggest worries. Nuclear weapons, and who controls them, would top the agenda during discussions with Mr. Baker, Shevardnadze said. Baker is also scheduled to hold talks with republican leaders. "Right now everything is normal but what will happen ... it's not a simple question," Shevardnadze said of Soviet nuclear weapons. "In this situation, there's a need to define who will be able to push the ominous button."