A TENTATIVE economic agreement reached by 12 Soviet republics may provide new momentum to conclude a political union treaty. But some republican officials say serious problems must be overcome before the economic treaty is implemented.Following a meeting in Alma-Ata, capital of the Central Asian republic of Kazakhstan, leaders of the 12 republics said Tuesday they were prepared to create an economic commonwealth. The three-year agreement would govern such spheres as taxation, banking, customs, and energy. "The establishment of this economic commonwealth gives us the basis to pull the country out of crisis without bloodshed," said Kazakhstan President Nursultan Nazarbayev. The three newly independent Baltic republics - Latvia, Lithuania, and Estonia - are refusing to sign on as full members in the treaty. Latvia, which had a representative at the Alma-Ata gathering, said it might become an associate member. Ivan Silayev, chairman of the Inter-republican Economic Committee now running the Soviet economy, said eight republics would sign a final version of the economic agreement by Oct. 15, the Interfax news agency reported. The rest would sign after further discussions. Mr. Silayev and Mr. Nazarbayev said the outcome in Alma-Ata could give new impetus to the formation of the Union of Sovereign States - President Mikhail Gorbachev's vision for a revamped, democratic confederation. That treaty has run into opposition in some republics. "After the signing of the economic treaty, it will become easier to work out the political aspects of a new union of sovereign states," Silayev said. Opposition prompted Mr. Gorbachev on Monday to threaten to resign if progress was not made soon on the union treaty. Presidential press spokesman Andrei Grachev said Monday that work on the treaty was proceeding, and a draft could be ready by the middle of October. However, some republican leaders think central authorities may be jumping the gun on the political union issue, saying the conclusion of the economic pact was no sure thing. They say two issues still need to be worked out - privatization of property and currency. A deadlock on either matter could quickly sink the treaty, said representatives from the Ukraine. In addition, the economic agreement will require republican parliamentary approval, something that can't be guaranteed in the Ukraine, said deputy Supreme Soviet Chairman Vladimir Grinyov. Eight republics pledged to sign the economic treaty before Oct. 15: Russia, the Ukraine, Byelorussia, Kazakhstan, Turkmenia, Tadzikistan, Uzbekistan and Kirghizia. All the republics except Russia, Kazakhstan, and Turkmenia have declared independence in one form or another.