Most elderly or disabled Americans in the Medicare insurance program now have prescription drug coverage, U.S. health officials said Wednesday, five days before an enrollment deadline for its Medicare drug benefit, but critics challenged the tally.

The figures, showing 37 million of 42 million beneficiaries have coverage under the new Medicare benefit or from other sources, came in the final days before the Monday deadline and immediately drew fire from critics.

Opponents, who contend the voluntary Part D benefit is too complicated and can lock older adults into a plan that does not cover their medicines, said the Bush administration is not giving clear numbers about how many people still lack coverage.

Of the 37 million participants, 8.9 million signed up on their own for a drug plan. The government also counted 5.8 million who get their medicines from programs other than Part D. The rest were automatically transferred from a prior drug program to the Medicare plan or were getting coverage from a former job, although retiree plans now get Medicare subsidies.

President George W. Bush, Health and Human Services Secretary Mike Leavitt and other officials are touring the country this week to try to boost enrollment. The program allows private insurers and health plans to offer coverage, with oversight by the Medicare. Until this law was enacted, the Medicare government health insurance program for older Americans did not cover most prescription drugs.

Health insurers and other companies also have launched a last-minute advertising blitz. UnitedHealth Group Inc., Humana Inc., and Aetna Inc., among others, all offer plans. Shares of all three companies closed up more than 4 percent on Wednesday.

Democrats and other critics said low income seniors are brushed aside in the latest estimates.

Robert Hayes, president of the advocacy group Medicare Rights Center, said Wednesday's count wrongly inflated its 37 million total. About half of Medicare beneficiaries, nearly 51 percent, who did not have drug coverage before still lack it, he said.

Families USA Executive Director Ron Pollack said the government report "plays fast and loose with the numbers."

Except for those with low incomes, Medicare beneficiaries who do not sign up by Monday must wait until November to enroll in the plan and will face added fees.

"We have a shot this week to get 90 percent of the people eligible enrolled" before then, Leavitt told reporters in a conference call from Michigan. Still, Leavitt acknowledged some may simply choose not to participate for personal reasons.