A brewing Senate rebellion against President Bush’s proposed savings in the Medicaid health program for the poor gained strength on Wednesday and some senators said they think they have enough votes to restore the spending.

A vote, expected Thursday, would be a rebuke to Bush’s budget priorities and an obstacle to a final House-Senate agreement on a budget framework for the next fiscal year.

Oregon Republican Sen. Gordon Smith said he believed that he and co-sponsor Sen. Jeff Bingaman, a New Mexico Democrat, had the 51 votes needed to restore $15 billion of Medicaid spending in the budget currently being debated by the Senate.

Smith’s amendment would also create a nonpartisan commission to studying how to modernize and change the joint federal-state health program for the poor.

Under the budget plan, Medicaid would still grow about 7.2 percent a year during the next five years. Without any changes, the rate would be about 7.4 percent.

Smith said it was wrong to risk pushing poor, disabled, and mentally ill people into the ranks of the uninsured where they would get costly and less suitable care in emergency rooms.

“I’m determined not to leave out these vulnerable Americans,” he said, adding that he supported Medicaid reform but believed a commission was a better path than a budget ax.

Several lawmakers and aides said if the Senate added $15 billion in spending, the House might well resist.

Some Republicans took issue with Smith, saying changes could not wait. Tennessee Republican Sen. Lamar Alexander said if a fiscal tsunami was hitting Medicaid, “the prudent thing is to move to higher ground.”

Secretary of Health and Human Services Mike Leavitt told reporters he disagreed with Smith and Congress needs to change Medicaid this year to give governors more flexibility.

Leavitt, a former Utah governor, said state governors are hampered by the “rigid inflexibility Medicaid operates under.”

He said he also favors changing the Medicaid drug payment formula, ending “creative accounting” by states, and tightening asset rules for Medicaid coverage of nursing homes.