Fifteen years after a Union Carbide pesticide plant leaked a poisonous gas that killed at least 7,000 people in Bhopal, India, and permanently injured tens of thousands more, survivors and relatives of victims filed suit yesterday against Union Carbide and its former chair in federal court in Manhattan. The suit seeks unspecified damages and wants the U.S. federal court to take back control of litigation that was moved to India in 1986. The plaintiffs charge that Union Carbide failed to obey rulings by courts in the U.S. and India and that company officials have failed to appear in Indian court to respond to criminal charges. The Indian government’s civil case against Union Carbide was settled in 1989 for $470 million, but many victims and their relatives have yet to receive compensation because of legal and bureaucratic tangles.