Legislation that would escalate the battle against radon, the gas estimated to cause up to 20,000 lung cancer deaths each year, was introduced in Congress. Radon, an odorless radioactive gas produced by the decay of natural uranium deposits, has been identified as the nation's No. 1 environmental cancer risk. Sens. Arlen Specter (R-Pa.), George J. Mitchell (D-Me.) and John H. Chafee (R-R.I.) sponsored legislation to authorize $30 million for a program of research and detection, and Rep. Thomas A. Luken (D-Ohio) announced a bill ordering federal assistance for state radon programs.