WASHINGTON  President Obama scored a big victory on Thursday as the Senate Finance Committee rejected a proposal to require pharmaceutical companies to give bigger discounts to Medicare on drugs dispensed to older Americans with low incomes.

The victory came at the expense of senators in Mr. Obama’s own party who had championed the proposal. The vote, in effect, upheld a deal reached in June by the White House and the drug industry, which saw the agreement as a possible way to avoid more onerous requirements that might be imposed by Congress.

The proposal, an amendment by Senator Bill Nelson, Democrat of Florida, would have required drug makers to provide Medicare with discounts in the form of rebates totaling more than $100 billion over 10 years.

Some of the money would have been used to close a gap in Medicare coverage of prescription drugs. In 2007, more than eight million Medicare beneficiaries fell into the gap, known as the doughnut hole.