CANBERRA, Feb 5 (Reuters) - Australia's upper house of parliament passed a vote of no confidence in Prime Minister John Howard on Wednesday for his handling of Iraq, illustrating the deep divide in Australia over joining any war.

Howard, a staunch U.S. ally, has come under attack for sending troops and approving fighter jet deployments to join U.S. and British forces in the Gulf preparing for a possible war on Iraq before the United Nations process has run its course.

Opposition and minor parties, who hold the balance of power in the 76-seat Senate, joined forces to pass the upper house's first vote of no confidence in a government or leader in its 102- year history. It was a symbolic gesture that has no legislative clout.

"This is a historic vote by the Senate, albeit on party lines as such motions always are," Australian Greens Senator Bob Brown told reporters after the vote was passed by 33 to 31 votes.

"John Howard has let this nation down. His gross mishandling of Australia's involvement deserved the strongest parliamentary rebuke."

But a bid by the left-leaning Greens to amend the no-confidence motion to condemn any Australian involvement in Iraq, with or without a U.N. mandate, was defeated when the main opposition Labor party voted with the conservative government.

Canberra has yet to commit itself to joining any military action in Iraq, whether U.N.-approved or U.S.-led, but Howard's decision to pre-deploy troops opened up a sharp political divide on the issue and prompted public protests.

Recent opinion polls show an overwhelming majority of Australians -- 76 percent -- oppose Australian participation in a U.S.-led war on Iraq while 57 percent support joining military action that has U.N. backing.

About 400 anti-war protesters demonstrated outside the national parliament on Tuesday as politicians, back from their summer break, began an emotional debate on Iraq, questioning Howard's unwavering support for the tough U.S. stance on Iraq.

Meanwhile a group of women in Lismore, 600 km (370 miles) north of Sydney, announced plans to follow the example of some U.S. and British protesters and strip off for peace this weekend in a "Disrobe to Disarm" protest.

Protest organiser, Australian singer Grace Knight, told Australian radio that hundreds of women were expected to bare all for an aerial photo shoot, using their bodies to spell out an anti-war message. The resulting photo will be sent to Howard.