Medicare payment cuts will leave more than half of clinics and doctors’ offices that provide cancer chemotherapy unable to cover costs of some key drugs, oncologists said on Wednesday.

The reductions may be close to double what the government anticipates, according to a survey of pricing data by the American Society of Clinical Oncologists.

The Centers for Medicare and Medicaid Services has estimated an 8 percent average cut in reimbursements for chemotherapy and other medicines. ASCO concluded the reduction would average 15 percent for the 100 practices it surveyed.

CMS Administrator Mark McClellan said officials were reviewing ASCO’s data and had not yet set final payment levels.

“The goal here remains to make sure we are paying accurately” for drugs and services and “to make sure there is high-quality access to the medicines our patients need,” McClellan told reporters during a conference call.

Changes in the way Medicare calculates payments to oncologists were mandated as part of last year’s law to overhaul the federal health insurance for the elderly and disabled.

Supporters said they needed to correct overpayments to physicians for the injected drugs that Medicare now covers. Medicare will start covering a broad range of prescription drugs in 2006.

Oncologists argued they relied on the inflated payments for medicines to cover costs of related services that Medicare did not fully cover, such as nutritional and psychological counseling.

Steep cuts may limit access to cancer care outside of hospitals in clinics and doctors’ offices, which usually offer more personal care and are closer to where patients live, said Ellen Stovall, president of the National Coalition for Cancer Survivorship.

Patients “may not go without treatment, but I worry they will go without care. What happens in a hospital setting is so very, very different from the care that is provided in a community oncology office,” Stovall told reporters during a conference call.

ASCO briefed congressional staff on its findings and is lobbying lawmakers to keep drug payment rates at current levels.

Prices that doctors pay for cancer drugs vary throughout the country.

The ASCO survey found 70 percent of medical practices will have to pay more next year for pamidronate, which is used to treat advanced cancers that have spread to the bone.

Seventy-three percent will not be able to cover the costs of the drug epoetin to treat anemia, a common side effect of chemotherapy.

And more than half said they will have to pay more than Medicare reimburses for irinotecan, a key colon cancer drug, and gemcitabine, used to treat lung and pancreas cancers.