Two health trade groups will begin airing dueling ads in their fight over Medicare as lawmakers face pressure to reverse scheduled cuts in doctor fees. America's Health Insurance Plans' ads say reducing payments to UnitedHealth Group Inc. and other private insurers through Medicare Advantage could push millions of seniors out of their current coverage. On the other side, the American Medical Association is airing new television and radio ads in six states that targets a group of senators who blocked action on the proposed legislation.