President Clinton's proposed Medicare prescription benefit would have markedly different effects on consumers depending on their income and circumstances, defying easy generalizations about whether it's a good deal.

"It's really hard to know whether or not it's going to be something that Medicare beneficiaries will deem affordable," said Tricia Smith, chief federal health lobbyist for the AARP. "They're going to have to assess their own circumstances and weigh the trade-offs."

The plan is intended to narrow a glaring gap in the federal health insurance program for the elderly and disabled. Though drugs play a key role in medical care, and research has produced a vast array of costly new ones, the standard Medicare package doesn't cover outpatient prescriptions.

Many Medicare beneficiaries now receive prescription benefits through employer-sponsored retiree health plans, privately purchased supplemental insurance known as "Medigap" policies, or managed-care plans such as health maintenance organizations that serve as alternatives to standard Medicare coverage. But an estimated 35 percent of Medicare enrollees have no drug coverage.

The question is whether the proposed prescription benefits would be more affordable than what some people have now.

Charles Bowden of Silver Spring and his wife, Gloria Tingling-Bowden, face crushing prescription expenses, but they said Clinton's plan wouldn't help. On $22,488 of income, the monthly premiums of about $24 each and the 50 percent copayments would be beyond their reach, they said.

Tingling-Bowden, 72, has drug coverage through an HMO, but she used up her $1,000 annual benefit in April. "By the time we pay out our rent and our other expenses, there's hardly anything left over for food, so there's no way in the world that we could afford to pay $24 a month," she said.

Under Clinton's proposal, Medicare beneficiaries could purchase prescription coverage for a monthly premium of about $24 in 2002, which would rise to $44 by 2008. Medicare would then pay half the cost of their prescriptions, within limits. Initially, Medicare would pay as much as $1,000 a year to match $1,000 of spending by the consumer. By 2008, the maximum Medicare payment would rise to $2,500.

For people with incomes below 135 percent of the poverty level -- $11,000 for individuals or $15,000 for couples -- Medicare would waive the monthly premium and the 50 percent copayment. Those with incomes between 135 percent and 150 percent of the poverty level also would qualify for a premium subsidy.

As in managed-care plans, patients could be steered toward particular brands of medicine or generics. But the White House said doctors could order drugs that aren't on the lists if medically necessary.

Although the administration has stayed away from the controversial idea of price controls, the program nevertheless is intended to enable the Medicare population to share the kind of discounts now enjoyed by people covered through large corporations and other groups -- savings of more than 10 percent, the administration said.

Compared with Medigap policies, the Clinton plan offers major advantages. The proposed premium would amount to $288 a year initially, much less than the $1,236 a 65-year-old in Virginia might pay for one of several Medigap policies that include prescription coverage. What's more, Medigap premiums can increase as the beneficiary ages, so that a policy costing $70 a month at age 65 can cost $130 a month at age 85.

Medigap policies pay 50 percent of drug costs up to a maximum payout of either $1,250 or $3,000 annually, depending on the policy. But before the supplemental insurance pays anything, the consumer must pay an annual deductible of $250, which isn't matched.

"When fully implemented, the [proposed] benefit will be more generous than what people are getting right now through Medigap, and the premiums will be a fraction of the cost," said Michael E. Gluck, director of health policy studies at the National Academy of Social Insurance.

Even so, Clinton's plan won't do any good for people who can't pay their share. When monthly costs can run $100 a month for an ulcer treatment, $200 a month for a drug to lower cholesterol, or $1,000 a month for an arthritis medicine, a 50 percent copayment can be prohibitive.

For people who receive prescription coverage through Medicare HMOs, the comparison is mixed. Many HMOs offer drug coverage at no extra charge, subject to annual limits on coverage and copayments that range from $5 to $35 per prescription. In the Washington area, for example, the Medi-CareFirst HMO's drug benefit features a $50 deductible, a $15 copayment per prescription, and a $1,000 maximum payout. On the first $1,000 of drug expenses, a patient with the typical 19 prescriptions a year would shell out $335 in the HMO, versus $788 under the first year of Clinton's plan. But the Clinton plan would continue to pay half of the next $1,000, after the patient would have exhausted the HMO benefit.

For Medicare beneficiaries who receive supplemental drug coverage from big employers, the Clinton plan would generally be a step down. At large companies, retiree benefits typically feature no deductibles, copayments of $15 or less, and unlimited coverage, said Frank McArdle, a principal of Hewitt Associates, which advises corporations on employee benefits.

By creating a Medicare drug benefit, analysts say, the government could encourage employers to stop providing supplemental coverage. White House officials said Clinton's plan would include incentives for employers to continue offering coverage at least as generous as the administration's proposal, but they didn't provide details.

In tailoring the plan to serve the entire Medicare population, the administration chose not to concentrate help on those most in need, such as the most severely ill. For 13 percent of Medicare beneficiaries, what they and their insurers spend on prescriptions this year will equal or exceed the $2,000 ceiling in Clinton's plan, according to a recent study by Gluck's organization.

"It's going to be a relatively small number of people, but to the extent they are low or middle income, they will be at risk," said Gail R. Wilensky, who chairs Congress's Medicare Payment Advisory Commission.