The Senate effort to adopt a new prescription drug plan stalled as Republicans thwarted Democratic efforts to take up a generic drug bill.

Debate on the bill, which would ease access to lower-cost generic drugs, had been scheduled to begin Tuesday morning. Democrats have said they intend to start consideration of the generic drug bill and then add a Medicare prescription drug benefit to it.

But late Monday, Sen. Judd Gregg, R-N.H., objected when Senate Majority Leader Tom Daschle tried to bring the bill up, saying there were still outstanding disagreements that needed to be worked out.

Democrats accused Republicans of stalling.

"The first I heard there was an objection was five minutes before," said Sen. Edward Kennedy, D-Mass. and chairman of the Senate Health, Education, Labor and Pensions Committee. "To delay something that is as important as this, I think is not warranted or justified."

Under the rules of the Senate, the earliest the Senate can try to take up the bill would be Wednesday and 60 votes would be needed to overcome GOP objections.

"There is no desire on anybody's part to slow this legislation up," Sen. Tim Hutchinson, R-Ark., insisted.

The dispute came as lawmakers scrambled to get enough votes for three competing Medicare prescription drug proposals, none of which currently has the 60 votes needed for passage.

Two Republicans, Sens. John Ensign of Nevada and Chuck Hagel of Nebraska, entered the fray Monday by offering a 10-year, $160 billion proposal, the least expensive so far.

That plan relies mostly on a Bush administration proposal to have seniors buy private discount drug cards at $25 a year for savings. Government help would kick in once a senior citizen reached limits set according to income. For instance, the poorest seniors would have a $1,500 cap. After the cap was met, a beneficiary would pay no more than 10 percent of the cost of each prescription.

Hagel called the plan affordable for senior citizens and taxpayers. "We believe it is the best approach," he said.

A tripartisan group that includes several Republicans, along with Democratic Sen. John Breaux of Louisiana and Sen. James Jeffords of Vermont, the Senate's lone independent, also made a last-ditch effort to sway Democratic leaders to support their bill -- a plan that would cost $370 billion over 10 years.

Senate Democrats, who control the chamber, are backing a $500 billion plan.

"Unfortunately, partisanship today jeopardizes any chance of sending Medicare prescription drug legislation to the president," said Sen. Olympia Snowe, R-Maine. "We're trying to break the partisan logjam."

The House has already passed a proposal that would spend $320 billion over 10 years on a prescription drug benefit. Another $30 billion in givebacks to Medicare providers is included in the House bill.

The tripartisan proposal relies on private insurers to administer the benefit, similar to the House plan. Beneficiaries would pay a monthly premium of $24 and have a $250 yearly deductible. Once the deductible was met, the government would pay 50 percent up to $3,450 in drug spending.

Everyone except the poorest beneficiaries would then be responsible for costs until they reached $3,700 in spending -- a gap of about $250. Once that cap was reached, the government would pay 90 percent of costs, with the beneficiary picking up the remaining 10 percent.

Senate Democrats have offered the more generous of the proposals. That plan would require beneficiaries to pay a $25 monthly premium and a $10 co-payment on generic drugs or a $40 co-payment on brand-name drugs. Out-of-pocket expenditures would be capped at $4,000 a year.

Both the tripartisan and Senate Democratic plan offer additional help for the poorest elderly Americans.