THE leaders of republics remaining within the Soviet Union agreed Sept. 16 to act as a single country when it comes to receiving food and economic aid from abroad.The decision is an obvious attempt to ease Western confusion over where to send aid under conditions of political disintegration and to ease Western concerns that aid will be wasted in the collapsing Soviet distribution system. But the State Council meeting attended by Soviet President Mikhail Gorbachev and leaders of 10 republics also revealed serious differences among them that may take months or longer to resolve. Most of the meeting was devoted to ensuring food supplies and discussing a draft treaty of economic union. The republics decided to act together when it comes to reaching agreements and signing contracts for delivery of food and consumer goods from abroad. The Committee on Economic Management, which now functions as the only form of central government, has been authorized to act on behalf of the republics in talks with foreign partners. Committee Deputy Chairman Yuri Luzhkov, who is in charge of the food supply effort, flew to Brussels and London yesterday for talks on aid. He will meet with officials of the European Community, from whom the Soviet leaders have requested $6 billion-$7 billion in food aid to get through the winter. He will also meet with representatives of the Group of Seven leading industrial nations in London to talk about emergency economic aid, Tass news agency reported. Russian Premier Ivan Silayev, who heads the management committee, expressed optimism after the meeting that the country will survive the winter. But according to Tass, he also warned republics about causing "unnecessary problems that would provoke conflict." The Council's statement on food supplies calls for doing "everything to make the farmer a real master of the land, the means of production and manufactured products." It envisions as-yet-undefined steps to stimulate production with market incentives and to reduce the gap between the prices of agricultural goods and industrial products. An illustration of the kind of problems facing the country was provided Monday by an ultimatum issued by collective farms in Eastern and Western Siberia complaining of unequal treatment and the effect of "the disintegrating system of material supplies," Tass reports. The farms are demanding subsidized prices for farm products, loans with easy terms, exemption from a 5 percent sales tax, and a doubling of farm workers' wages. Unless their demands are met, the farm organizations told the Russian republican government they will stop selling food to the government. Because of similar actions by farms nationwide, the government has procured only about 25 million of the estimated 85 million tons of grain needed to supply cities through the winter, Soviet officials say. THE president of the Central Asian republic of Turkmenia, Saparmurad Niyazov, made a somewhat similar threat in an interview with Tass Sept. 16. He complained that republics were reneging on agreements to deliver feedstocks for their livestock. If these deals are not honored, he warned, "we will be compelled to sell our cotton, oil, and gas on the world market in exchange for fodder." The key to resolving these conflicts lies in an agreement on a treaty of economic union. The Committee on Economic Management's deputy chairman, Grigory Yavlinsky, presented his draft of that treaty to the State Council meeting, which agreed to accept it in principle. But republican delegations will go to work on the document in a process Mr. Yavlinsky says will take at least one more month. "The work has begun in principle. And judging by the discussion, this work will be very complicated," Yavlinsky told Soviet reporters after the meeting. "It is true," Yavlinsky admitted to the Nezavisimaya Gazeta, "that many republican leaders are not inclined to support our project. Georgia is saying bluntly, 'First recognize our independence and then we will sign the economic agreement.' But that is a blind alley for us." Georgia, along with Moldavia and the three now-independent Baltic states, did not attend the State Council meeting. But even among those at the session, there was criticism of the Yavlinsky draft. Kirghizian President Askar Akayev proposed that the treaty be phrased more generally, along the lines of the international agreement that established the European Community. But the republican leaders agreed, Yavlinsky said, to have a more concrete document.