A top Consolidated Edison official said today that the radioactive leak at the Indian Point 2 nuclear plant in February might have been avoided if the plant's most recent inspection had employed the kind of advanced technology that was available but not yet widely used by the industry. Speaking at a meeting of the Nuclear Regulatory Commission in suburban Washington, James S. Baumstark, a vice president of engineering for Con Edison, offered the fullest account to date as to why a corroded tube in one of the plant's steam generators cracked on Feb. 15, allowing radioactive water to mix with clean water and forcing the utility to shut the plant down.