Want an appointment with kidney specialist Adam Weinstein of Easton, Md.? If you're a senior covered by Medicare, the wait is eight weeks.

How about a checkup from geriatric specialist Michael Trahos? Expect to see him every six months: The Alexandria-based doctor has been limiting most of his Medicare patients to twice yearly rather than the quarterly checkups he considers ideal for the elderly. Still, at least he'll see you. Top-ranked primary care doctor Linda Yau is one of three physicians with the District's Foxhall Internists group who recently announced they will no longer be accepting Medicare patients.

"It's not easy. But you realize you either do this or you don't stay in business," she said.

Doctors across the country describe similar decisions, complaining that they've been forced to shift away from Medicare toward higher-paying, privately insured or self-paying patients in response to years of penny-pinching by Congress.

And that's not even taking into account a long-postponed rate-setting method that is on track to slash Medicare's payment rates to doctors by 23 percent Dec. 1. Known as the Sustainable Growth Rate and adopted by Congress in 1997, it was intended to keep Medicare spending on doctors in line with the economy's overall growth rate. But after the SGR formula led to a 4.8 percent cut in doctors' pay rates in 2002, Congress has chosen to put off the ever steeper cuts called for by the formula ever since.

This month, the Senate passed its fourth stopgap fix this year - a one-month postponement that expires Jan. 1. The House is likely to follow suit when it reconvenes next week, and physicians have already been running print ads, passing out fliers to patients and flooding Capitol Hill with phone calls to convince Congress to suspend the 25 percent rate cut that the SGR method will require next year.

Such temporary reprieves have increased the potential pain down the road, compounding not only the eventual cut but the cost of doing away with it for good, now estimated in the tens of billions.

The lobbying blitz by doctors also comes amid concern in Washington that Medicare spending is spiraling up so fast the nation can't afford to boost it further by significantly raising doctors' pay. And government analysts and independent experts suggest that although doctors could not absorb a 25 percent fee cut, the claim that they have been inadequately compensated by Medicare until now is wildly exaggerated.

Among the top points of contention is the complaint by doctors that Medicare's payment rate has not kept pace with the growing cost of running a medical practice. As measured by the government's Medicare Economic Index, those expenses rose 18 percent from 2000 to 2008. During the same period, Medicare's physician fees rose 5 percent.

"Physicians are having to make really gut-wrenching decisions about whether they can afford to see as many Medicare patients," said Cecil Wilson, president of the American Medical Association.

But statistics also suggest many doctors have more than made up for the erosion in the value of their Medicare fees by dramatically increasing the volume of services they provide - performing not just a greater number of tests and procedures, but also more complex versions that allow them to charge Medicare more money.

From 2000 to 2008, the volume of services per Medicare patient rose 42 percent. Some of this was because of the increasing availability of sophisticated treatments that undoubtedly save lives. Some was because of doctors practicing "defensive medicine" - ordering every conceivable test to shield themselves from malpractice lawsuits down the line.