MIAMI - Insurers constantly caution seniors that Medicare Advantage benefits such as hearing aids, dental payments, and gym memberships will fizzle if Democrats get their way and cut government subsidies for them.

But tens of billions of Medicare dollars funneled through insurers also pay for extras that never reach beneficiaries: multimillion-dollar salaries, executive retreats in Hawaii, Scotland, and Cancun; and massive spending on marketing to lure more customers to the privately administered Advantage plans that serve as an alternative to government-provided Medicare.

The government-subsidized benefits that seniors on Advantage plans receive - often at premiums lower than Medicare premiums - are real, and are in danger in some cases if the health-care overhaul working its way through Congress is enacted.

Medicare Advantage subsidies are slated to be reduced to pay for the overhaul. Though there are marked differences between House and Senate versions, both would lower payments to private Medicare Advantage plans, which on average cost the government 14 percent more than traditional Medicare.

The harshest critics of the Advantage program say patients are exchanging hassle-free coverage for plans that offer cheap extra benefits but may ultimately deny them necessary treatment.

"They're giving special benefits that are valuable," said Mary Johnson, policy analyst for the Senior Citizens League, a nonpartisan, 1.2-million-member group. "But what people don't understand are the trade-offs."

AARP, which lends its name to a Medicare Advantage plan, and other senior advocacy groups support the Advantage cuts. Still, it is likely that at least some seniors will see their premiums rise, their benefits cut, or their plans close.

Despite the belief that Advantage plans offer broad savings for seniors, the Government Accountability Office last year found wide differences depending on the plan.

A half-million Advantage enrollees were in plans with no co-pay for hospital stays. But a roughly equal number were in plans with high hospital co-pays and no limits on out-of-pocket inpatient expenses, which could potentially cost patients thousands more.

The disparity was greatest for some of the sickest seniors, those who return to the hospital within 60 days of discharge, the GAO found. Under traditional Medicare, those patients would pay no deductible. Under many Advantage plans, the deductibles can be steep.

Many of the benefits offered by Advantage plans are relatively cheap. Vision coverage cost insurers $3.37 a person each month, on average, according to 2007 filings with the government. Hearing coverage cost less than a dollar.

Insurers participating in the Advantage program responded to inquiries by Senate Democrats that led to a report this month providing some fuel in their effort to trim the subsidies. The companies reported, on average, spending more than 15 percent of premium revenues on profits, marketing and corporate expenses, nearly 10 times as much as traditional Medicare.