But Senate Democrats are signaling they may block the nomination, in an attempt to pressure the Bush administration to hand over documents about Mr. Bolton's past handling of classified intelligence matters.
Critics of Mr. Bolton allege that he mistreated subordinates while serving as the chief U.S. diplomat for arms control. He is also accused of pressuring analysts to reach certain conclusions on intelligence matters.
In the past, Mr. Bolton has been a critic of the United Nations.
On Wednesday, a senator from President Bush's own Republican party, Senator George Voinovich, of Ohio, also urged colleagues to reject Mr. Bolton.
But other Republicans say he is a tough and direct diplomat who can help reform the United Nations.