WASHINGTON, (UPI) -- Senate Democrats on Wednesday claimed growing support for extending the Medicare's enrollment deadline for the Part D prescription-drug plan.

Sign-up for the program ends May 15, after which seniors will have to pay a 1-percent-per-month penalty if they enroll late. Critics claim that the deadline is too soon given some seniors' confusion over Part D, which in many states offers 50 or more plan choices.

Democrats on Wednesday released a letter to Senate Majority Leader Bill Frist, R-Tenn., asking him to allow the Senate to debate an extension when Congress returns from its Easter recess next week. The letter was signed by 48 lawmakers, including four Republicans.

"In the short run, we need to at least give people more time," Sen. Debbie Stabenow, D-Mich., told reporters.

President Bush has publicly opposed any extension. Medicare chief Mark McClellan said in an interview Wednesday that there are "very good reasons for having the enrollment deadline."

McClellan suggested that as many as two million fewer seniors would sign up for Part D if the pressure of a deadline were removed.

Still, Democrats said they would increase their pressure for an extension and other changes to Part D as the deadline nears. The issues are likely to emerge in early May, when Frist is planning a week of floor action pushing GOP health priorities -- dubbed "Health Week" -- including small business health plans and medical malpractice insurance reforms.

Stabenow, a member of the Senate Finance Committee, said her party would use the debate to push amendments allowing the government to negotiate lower drug prices with pharmaceutical makers and to authorize importation of cheaper drugs from foreign countries.

"We intend to be bring up some of these broader issues at that time," she said.

The announcements came on the same day that insurance and pharmacy groups announced an agreement that they said would speed service for Medicare beneficiaries at pharmacy counters.

The groups announced that they had agreed on a way to standardize computer messages between drug plans and pharmacies to simplify prescription filling at the pharmacy counter. The plan is meant to reduce some confusion resulting from the dozens of private plans confronting seniors and pharmacies under Part D.

Seniors in most states are choosing between 40 -- and sometimes up to 60 -- private Medicare drug plans. That has led to complaints of confusion from beneficiaries, but also to angry reactions from pharmacists who face dozens of different standards for communicating with plans over coverage issues.

"The frustration that it causes ... I just can't tell you how frustrating it is," Bruce Roberts, president of the National Community Pharmacists Association, told reporters.

Under the agreement, insurers and pharmacies agreed to a single format for sending computerized messages back and forth when pharmacists need to check whether a drug is covered. Until now, those communications have kept pharmacists on the phone, sometimes for hours, while customers wait.

"It causes chaos in the pharmacy," Roberts said. "This will make a tremendous difference," he said.

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