Indian Prime Minister Indira Gandhi and French President Francois Mitterrand addressed the UN General Assembly Wednesday. Mrs. Gandhi, speaking on behalf of the world's nonaligned nations, called for a nuclear weapons ban. She also said the present world economic order was based on inequality. On Tuesday she had called for the formation of a new international monetary conference to replace the 1944 Bretton Woods agreement which set up the World Bank and the International Monetary Fund. During his speech, Mr. Mitterrand bitterly protested the US-Soviet nuclear arms reduction talks in Geneva ''without our consent.''