Doctors and pharmacists say many drugs theoretically covered by the new Medicare drug benefit are not readily available because of insurers' restrictions and requirements.

The benefit is administered by scores of companies under contract to Medicare. Each plan has its own list of covered drugs, known as a formulary. Drug plans require doctors and patients to obtain "prior authorization" for certain drugs on their formularies. 

The procedures vary by plan. One plan may have 25 or 30 forms for prior authorization for different drugs. Most states have at least 40 Medicare drug plans. 

Doctors say the diverse requirements are onerous and can delay or deny access to needed medications. But insurers say the requirements save money and promote the proper use of the medications. 

Dr. Jeffery A. Kerr, who cares for hundreds of older patients in southern Missouri, said: "Medicare drug plans have created significant hurdles that patients and physicians must jump over before getting their medications. The prescription drug plans are playing a dangerous game. In many cases, we're dealing with frail, very vulnerable individuals."

For years, commercial insurers and their pharmacy benefit managers have used similar techniques. But Dr. Kerr said the techniques used by some Medicare plans were more onerous and restrictive. They are also more noticeable, he added, because Medicare beneficiaries are high users of prescription drugs.

Dr. Steven A. Levenson of Towson, Md., president-elect of the American Medical Directors Association, which represents doctors who care for nursing home residents, said, "We have seen signs that Medicare drug plans are using management controls to deter access to medically appropriate drugs, including drugs on their own formularies."

Ross W. Brickley, a pharmacist in Kinston, N.C., said he had requested prior authorizations for hundreds of drugs taken by Medicare patients in more than 20 plans, each with its own policies, forms and procedures. 

"We have a world of chaos," Mr. Brickley said.

David W. Bernauer, chairman of Walgreen, one of the biggest drugstore chains, echoed that concern. 

"It is impossible for pharmacists to keep track of all these formularies" and prior authorizations, Mr. Bernauer said. 

The government, he added, "should use its leverage to promote greater standardization of policies and procedures."

In his radio address on Saturday, President Bush described the drug benefit as "a good deal for seniors." Those who enroll "will end up spending about half of what they used to spend on prescription drugs each year," Mr. Bush said.

Yet he acknowledged that problems had occurred. 

"Some people had trouble the first time they went to the pharmacy after enrolling," Mr. Bush said. "Information for some beneficiaries was not transferred smoothly between Medicare, drug plans and the states. And in the early days of the drug coverage, waiting times were far too long."

Several insurance executives said they had not realized that their companies required doctors to use many different forms for prior authorizations. "That can't be right," Francis S. Soistman Jr., executive vice president of Coventry Health Care, said when asked about the forms on his company's Web site. The site has 39 forms for doctors to use when prescribing certain drugs for Coventry Medicare plans, marketed under the name AdvantraRx.

At the top of each form is a logo that says, "AdvantraRx: Medicare prescription drug plans made easy."

After checking with Coventry pharmacists, Mr. Soistman said the forms were justified because "each drug requiring prior authorization has unique clinical criteria that must be met." The forms, he said, "serve as a checklist of necessary information needed for our review."

More generally, Mr. Soistman said, prior authorization limits the use of drugs with a potential for abuse like OxyContin and drugs with safety problems like Accutane, an acne treatment that can cause birth defects. In addition, he said, prior authorization is a way to prevent the overuse of high-cost medications and to ensure that "equally effective, less expensive agents are used first."

In its prior authorization forms, Coventry requires doctors to provide details of laboratory test results, "all office notes" and other data to show why certain drugs are needed.

For an osteoporosis drug, Forteo, the company wants to know the patient's bone mineral density, as measured by the "T score." For some AIDS drugs, the doctor has to specify the "viral load" and white blood cell count. In requesting approval for certain antifungal drugs, the doctor must provide a laboratory report identifying the species of the infectious agent.

Other Medicare plans focus on other drugs. The four principal drugs for Alzheimer's disease are all subject to prior authorization under some plans, including ones offered by RxAmerica, a subsidiary of Longs Drug Stores. 

Some companies require doctors to report the patient's score on a mental examination before covering certain drugs for Alzheimer's. Insurers say the test is needed to decide whether a patient is likely to benefit.

Dr. Daniel C. Lyons, senior vice president of Independence Blue Cross, said his company used "one standard prior authorization form" for its Medicare drug plans, sold in 13 states under the name AmeriHealth. He later confirmed that the company also had 17 forms for high-cost injectable drugs to treat complex conditions like cancer, hemophilia, H.I.V. infection and rheumatoid arthritis.

In an interview, Dr. Lyons said it would be desirable to "simplify and standardize the prior authorization process."

Dr. Mark B. McClellan, administrator of the Centers for Medicare and Medicaid Services, said last week that the program was "working smoothly for the vast majority of beneficiaries." He promised to repair problems within a few weeks.

"Plans are filling over a million prescriptions a day," Dr. McClellan said. "We are seeing improvements on a daily basis."

Medicare officials approved all the formularies last year. A former Medicare official, Babette S. Edgar, said the government had analyzed not only the lists of covered drugs, but also the tools to regulate access to those drugs. 

In the last year, the administration repeatedly assured beneficiaries that they would have convenient access to "all medically necessary drugs," though it gave insurers some leeway to define medical necessity.

Officials have developed a model form for beneficiaries to request coverage or prior authorization for a drug. The administration emphasized that "use of this model form is optional." A "Medicare drug plan may require additional information or documentation," it added. 

For more than a decade, health plans have been encouraging the use of generic drugs, mail-order pharmacy service and other techniques to control the costs of drug benefits. The efforts appear to be paying off for insurers and employers. The growth of prescription drug spending slowed to 8.2 percent in 2004, after nine years of double-digit increases, the government reported last month.

On the commercial side, insurers typically charge higher co-payments for certain drugs. But federal law limits charges for low-income Medicare beneficiaries. Medicare drug plans use other techniques. 

"The use of prior authorization is far more prevalent in Medicare than in commercial insurance programs," said John Feather, executive director of the American Society of Consultant Pharmacists, whose 7,000 members specialize in drug care for the elderly. 

Most drug plans say they cover more than 90 of the 100 drugs that Medicare beneficiaries commonly use. Dr. Charles A. Crecelius, a geriatrician in St. Louis, said, "Several of my patients were totally fooled" by such assurances.

A drug may be on the formulary but difficult to obtain because of the prior authorization and other rules, Dr. Crecelius said.