WITH one fell swoop, the Soviet Union has been dissolved as a unitary federal nation and replaced by a loose confederation of independent republics.An emergency session yesterday of the Congress of People's Deputies voted overwhelmingly to approve a radical restructuring of the Soviet state. Kazakhstan President Nursultan Nazarbayev, speaking on behalf of 11 Soviet republics and President Mikhail Gorbachev, presented the plan to the Soviet legislature. "We state that the failure of the coup and the victory of democratic forces have delivered a serious blow to reactionary forces and to everything that had been hindering the process of democratic changes," he pronounced. "Thus a historic chance has been created to speed up ... the renovation of the country." But the joint statement also reflected the growing awareness among Soviet and republican leaders that the country was on the verge of a chaotic breakup, deepening an already severe economic crisis and jeopardizing potential Western assistance. The situation after the attempted coup of Aug. 19-21 had effectively blocked the process of forming a new treaty of Union, Mr. Gorbachev and the republican heads admitted. They warned this could "lead to unpredictable consequences in the country and in relations with foreign states if it goes out of control." Until the creation of a permanent union treaty, passage of a new constitution, and elections, the leaders propose to dissolve the existing union institutions and replace them with an interim administration. The Soviet parliament, including the Congress which elects the sitting parliament from among its members, is asked to eliminate itself. It will be replaced by a council of representatives of the republics, with 20 deputies selected by each republican parliament. The central government will consist of a state council including the Soviet president and republican leaders to coordinate all domestic and foreign policy. An interrepublican economic committee, representing each republic equally, will coordinate economic reforms. The republican parliaments will discuss a draft constitution to be ratified by the new congress of republican representatives. Until new elections, republican leaders clearly see President Gorbachev's continuation in office as an important symbol of continuity. "We have to have something or someone around whom we can unite," Alexei II, Patriarch of the Russian Orthodox Church and a Congress member, told reporters yesterday. However, the fate of the huge central government bureaucracy is not clear. "Only the interrepublican economic committee will now be in charge of governing the country until a new union body is organized," Georgi Shakhnazarov, advisor to Gorbachev, told reporters. "Nobody knows whether there will be a cabinet or other form of political structure." The only central ministries which will clearly remain are the Foreign Ministry and those devoted to security, including the Defense Ministry, the KGB, Interior Ministry, and the Procurator's Office. But according to the agreement, all will be radically reformed. The republics will also sign an agreement on collective security to preserve a single Army, and they will abide by all the Soviet Union's international obligations, including arms control treaties and debt payments. "The armed forces will remain united," newly installed Defense Minister Air Marshal Yevgeny Shaposhnikov told reporters, "especially the strategic nuclear forces that will be directly subordinated to the center. No one should be concerned. If we managed to agree with the Americans, with the West Germans on many questions - including disarmament, withdrawal of troops - then we will certainly reach an agreement with our republics." Under the new structure, the union republics will seek to join the United Nations as individual members, along with membership for the union as a whole. The document is the product of a Sunday meeting between Gorbachev and the leaders of 11 republics. The declaration was signed by 10 republics: Russia, the Ukraine, Byelorussia, Uzbekistan, Kazakhstan, Azerbaijan, Kirghizia, Tadzhikistan, Turkmenia, and Armenia. Georgia, which had earlier refused to join a new union, participated in the talks but did not sign the statement. The deal is apparently aimed at calming non-Russian republics' fears that a post-coup administration will be dominated by Russian President Boris Yeltsin's government. "If Yeltsin acts alone it can provoke suspicions from other republics about possible imperial ambitions," Sergei Stankeivich, senior Yeltsin advisor, told reporters. "Gorbachev is necessary as a mediator in such a situation." The new structure basically accepts the full independence of the four republics who did not participate - the Baltic republics of Estonia, Latvia, and Lithuania, and the ethnic Romanian republic of Moldavia. But it also proposes that all republics immediately form an economic union to ensure that the economy functions, providing basic services and introducing market reforms, a structure that many compare to the European Community. The Baltics would be included. "It takes place at the initiative of the Ba ltic republics themselves," says Mr. Stankeivich. The question of Baltic independence, which is on the Congress agenda, is now a virtual fait accompli. The key problem in letting the Baltics go appears to be the huge Soviet military facilities there, particularly the Navy's Baltic Fleet. Stankeivich suggests that an agreement could be reached allowing some of the bases to remain and to regulate the functioning of the ports "which have not only a trade but strategic significance." Not everyone in the Congress is happy about this transformation of the union, not least because it means the disappearance of the Congress from the political scene. Conservative leader Yevgeny Kogan denounced the proposals as unconstitutional Referring to the republican leaders he charged that the parliament is now "reduced to a mouthpiece of the czar."