The Ukraine, the second most powerful Soviet republic, voted yesterday to join the accord setting down the principles of economic cooperation between the Kremlin and the republics.The agreement of the Ukraine, an economic and agricultural powerhouse of 52 million people, was seen as vital to the pact's survival. The accord, signed by the Kremlin and eight republics last month, delegates most economic decisionmaking to the republics, leaving Moscow to assume a coordinating role for finance, budget, energy, and other sectors. Moldavia and Azerbaijan have indicated their willingness to join, leaving only Georgia still outside the agreement. The proposal approved by the Ukrainian parliament authorizes the Ukrainian government to initial the economic accord, seen by Soviet President Mikhail Gorbachev as a stepping stone to a new looser confederation. The parliament will vote on ratification of the document once work on some 20 related agreements is completed. Many deputies predicted a new fight when the document comes before parliament for ratification.