Washington ? The Bush administration and GOP leaders on Thursday renewed their push for Senate approval of John Bolton as U.N. ambassador. Democrats maintained he is too brash and ineffective to be confirmed.

The sharp division all but guaranteed that lawmakers were headed toward another partisan showdown in the full Senate, although Democrats would not say whether their opposition would amount to a filibuster, as it did last year.

A Senate vote on Bolton could come as early as September, just as election season heats up with Bush’s foreign policy a major issue for voters. The United Nations has been at the forefront of international discussions on North Korea’s missile tests, Iran’s nuclear program and the crisis in the Middle East.

“I do believe, without any reservation whatsoever, that the Senate will and should give that advice and consent to this nominee because he becomes an integral member of the president’s national security team at a time when our nation is faced with these many complex issues,” said Sen. John W. Warner, R-Va.

After repeated failed attempts by GOP leaders to grant Bolton Senate approval, Bush last Aug. 1 used his executive power to sidestep Congress and temporarily assign Bolton to the job. Republicans decided to revive the matter this week after Sen. George Voinovich, R-Ohio, who last year sided with Democrats in opposing Bolton, announced he would support Bolton this time.

Several Democrats said during the nomination hearing Thursday that their views had not changed, citing reports that Bolton has alienated other ambassadors and failed to make progress on U.N. reform efforts.

“My concern is that at the moment of the greatest need for diplomacy in our recent history, we are not particularly effective at it,” said Sen. Joseph Biden, of Delaware, top Democrat on the Senate Foreign Relations Committee.

Biden and others did not say whether they would try to block an up-or-down vote in the full Senate as they did last year; such a move can be blocked by 60 of the 100 senators.