Under growing pressure, the administration refused repeatedly to state a position Tuesday on legislation formalizing President Barack Obama's oft-stated promise that people who like their existing coverage should be allowed to keep it under the new health care law. Senate Democrats spoke dismissively of the proposals, signaling they have no intention of permitting a vote on the issue that marks the latest challenge confronting supporters of "Obamacare." An earlier controversy appeared to be ebbing on a law that has generated more than its share of them. Even so, one strong supporter of the health care law, Sen. Sheldon Whitehouse, D-R. I., good-naturedly told an administration official, "Good luck getting through this mess."