Three senior Republican Senators put on the brakes Tuesday, voicing doubts about the wisdom of a Republican plan that combines cuts in the Medicare and Medicaid programs with a tax cut. Orrin Hatch, Alan Simpson and Alfonse D'Amato raised questions as the Senate Finance Committee began work on the GOP legislation. "I have never been for a tax cut for the rich or anyone else," Simpson said. D'Amato, whose constituents include millions of Medicare and Medicaid beneficiaries as well as a huge medical industry, seemed to agree with the Clinton Administration, saying that the Democrats' argument that the Republicans were cutting Medicare to pay for tax cuts "resonates and senior citizens are concerned. ... It's difficult to make the case that we are doing this to strengthen Medicare."