WASHINGTON — Bewildered by the complexity of the new Medicare outpatient prescription benefit, seniors will not be rushing to sign up, according to a comprehensive survey released yesterday as open enrollment draws near.

Although the government has spent more than $250 million to promote and explain the benefit, only 20 percent of seniors have made up their minds to enroll, the survey by the Kaiser Family Foundation and the Harvard School of Public Health found.

Another 37 percent said they would not sign up, while 43 percent said they had not decided what to do. The open enrollment runs Tuesday to May 15.

If the doubts harden into disdain, that could force major changes to one of President Bush's top domestic policy accomplishments.

"The potential is grim," acknowledged John Rother, policy director of AARP, the seniors' lobby, which lent critical support in winning congressional approval of the program.

"If only 20 percent or even 30 percent of seniors sign up, that is very negative for the future of the program, because the people most likely to sign up are the people with high drug expenses, and you don't have insurance if you don't spread the risk among people who are healthy," Rother explained.

The government has estimated that about two-thirds of seniors will sign up in the first year of the benefit. But many seniors appear to be stumped. There is "almost paralysis over what to do," said Maryann Brodie, polling director for Kaiser, which has cosponsored nine such surveys on seniors' attitudes toward the new benefit.

Many are confused by having to pick among dozens of private prescription plans that will be offering the government-subsidized benefit in each state, the survey found.

Others who may have drug coverage through a former employer, or who purchase it on their own, are not sure how to evaluate the costs and benefits of switching.

Those who delay beyond May 15 could face a penalty in the form of higher premiums in subsequent years.

"Beneficiaries are having a difficult time answering the most important question: 'What does it mean for me?'" said Drew Altman, president of the Kaiser foundation, a nonprofit organization that conducts healthcare research.

Medicare provides coverage for hospital care and doctor visits to more than 42 million elderly and disabled beneficiaries, but until now the program has not paid for outpatient prescriptions.

Barbara Potter, who's disabled and now gets Medicare benefits, told the Knight Ridder News Service that she had trouble getting information about the 46 Medicare drug plans available in her area.

"I've been a government contractor for years, so I'm used to bureaucracy, but this is just ridiculous," said Potter, a retired freelance health writer in Hornell, N.Y. "I am finding this the most labyrinthine experience I've ever had with government."

Health and Human Services Secretary Mike Leavitt said it was too early to make sweeping predictions about the success or failure of the drug plan.

Economists say the Medicare drug plan should be a good deal for most seniors, since the government will pick up three-fourths of the total cost of the program. Beneficiary premiums averaging about $32 per month will cover the rest.

However, because of budget constraints, Congress designed a complicated benefit. For instance, it has a coverage gap — nicknamed the "doughnut hole" — between $2,250 and $5,100 of annual expenses. Seniors must purchase supplemental policies to cover that.

Medicare administrator Mark B. McClellan pointed to another new survey that showed about half of seniors say they are likely to enroll.

But that survey, a Wall Street Journal Online/Harris Interactive poll, was done using the Internet; of the 2,160 responses collected from Oct. 26 to Oct. 28, 290 were from seniors. The Kaiser poll, conducted by telephone Oct. 13 to Oct. 31, found that 76 percent of the 802 seniors surveyed said they had never been online.

The Harris survey also found increasing doubts among seniors about whether they would be able to choose the right plan.

In the Kaiser survey, only 39 percent of Medicare beneficiaries said they thought the drug plan would benefit them personally, while 49 percent said it would not.

The Kaiser poll found that the sickest seniors were more likely to say that they will enroll. Among those who take more than four prescription medications a day, 25 percent said they would sign up. However, only 16 percent of those who take one to three medications daily said they would get the coverage.