Two powerful health trade groups will begin airing dueling ads this week in their fight over Medicare, hoping to influence Congress as lawmakers face pressure to reverse scheduled cuts in doctor fees.

America's Health Insurance Plans, a trade group of private insurers, is siding with Senate Republicans and the White House in their standoff with Democrats over a measure that would halt the cuts by trimming payments to private insurers. The ads, which will run on national cable television through the weekend, say reducing payments to UnitedHealth Group Inc. and other private insurers through a program called Medicare Advantage could push millions of seniors out of their current coverage.

"Millions more will have to pay higher out-of-pocket costs for health care and lose important benefits they depend on," the ads say.

On the other side, the American Medical Association said Tuesday it was airing new television and radio ads in six states through the week that targets a group of senators who blocked action on the proposed legislation. The bill passed the House but stalled in the Senate last week amid a veto threat by President Bush.

The ads, which will initially run in Mississippi, New Hampshire, Pennsylvania, Tennessee, Texas and Wyoming, open with a reference to Independence Day. They then say: "There's no celebrating for the millions of seniors, the disabled and military families who will lose their access to health care. A group of U.S. senators voted to protect the powerful insurance companies at the expense of Medicare patients' access to doctors."

Some 600,000 doctors who care for Medicare patients face a 10.6 percent fee cut. The reduction was scheduled to take effect Tuesday.

On Monday, the Bush administration said it would delay processing Medicare payments to doctors until at least July 15 to give Congress more time to find a solution, putting pressure on lawmakers to quickly find a compromise when they return to work the week of July 7.

Only Congress can block the cut to doctors' payments. The proposed legislation, which passed the House 355-59 and fell one vote short in the Senate, has broad support from doctors, hospitals and pharmacists but is strongly opposed by the insurance industry.

About 80 percent of the some 44 million elderly and disabled people on Medicare have their health bills paid by the traditional fee-for-service program; about 20 percent, or 8.7 million, get their benefits through private health plans that receive payments under the Medicare Advantage program, according to a 2007 fact sheet by the Kaiser Family Foundation.

Democrats this year have focused on taking the money from the Medicare Advantage program, which lets the elderly and disabled get their health benefits through a private insurer rather than through traditional Medicare.

Democratic lawmakers say the government's payments to the insurers are overly generous, but the administration and supporters in Congress say the payments translate into lower monthly premiums for Medicare Advantage participants or extra services such as vision and dental care. Under the bill passed by the House, insurers would lose nearly $14 billion over five years.