By Tabassum Zakaria and Susan Cornwell

WASHINGTON (Reuters) - A U.S. House committee approved on Wednesday a resolution calling the 1915 massacres of Armenians genocide, brushing aside White House warnings that it would do "great harm" to ties with NATO ally Turkey, a key supporter in the Iraq war.

The House of Representatives Foreign Affairs Committee approved the resolution 27-21. It now goes to the House floor, where Democratic leaders say there will be a vote by mid-November. There is a companion bill in the Senate, but both measures are strictly symbolic and do not require the president's signature.

Turkey calls the resolution, which was proposed by a lawmaker with many Armenian-Americans in his district, an insult. Ankara rejects the Armenian position, backed by many Western historians, that up to 1.5 million Armenians suffered genocide at the hands of Ottoman Turks during World War One.

Turkey has warned of damage to bilateral ties and military cooperation if Congress passes the measure. President George W. Bush and his secretaries of state and defense warned against the step, as did a number of former U.S. secretaries of state.

"This resolution is not the right response to these historic mass killings, and its passage would do great harm to our relations with a key ally in NATO and in the global war on terror," Bush said at the White House before the vote.

The bulk of supplies for troops in Iraq pass through Turkey's Incirlik airbase, and Turkey provides thousands of truck drivers and other workers for U.S. operations in Iraq. Supplies also flow from that base to troops in Afghanistan.

Advocates of the resolution said Turkey should simply acknowledge history and stop threatening retaliation.

"I think our relationship is important enough to the United States and Turkey to survive our recognition of the truth," California Democratic Rep. Adam Schiff, the chief sponsor, said in an interview after the vote.

The committee vote followed hours of sometimes emotional debate over whether, as the panel's chairman Rep. Tom Lantos said, lawmakers should "condemn this historic nightmare through the use of the word genocide." or put military cooperation with an upset Turkey at risk.

NEED TO 'CLEAN OUR OWN HOUSE'

Lantos, a California Democrat and Hungarian-born Jew who survived the Nazi Holocaust, voted for the resolution.

Some lawmakers said backers were hypocrites or just plain "crazy," as Rep. Dan Burton, an Indiana Republican, put it.

"We're talking about stiffing the one ally that is helping us over there (in Iraq). It just doesn't make any sense," Burton told a packed hearing room. The audience included Turkish officials and elderly survivors of the massacres.

Rep. Gregory Meeks, a black Democrat from New York, said Congress should focus on the failings of U.S. history, such as slavery or the killings of Native Americans.

"We have failed to do what we're asking other people to do ... We have got to clean up our own house," said Meeks, who voted against the resolution.

Turkey's ambassador to the United States, Nabi Sensoy, told reporters after the vote he did not want to prejudge what his government would do. "We are disappointed at this point, but this process is going on," he said.

The White House was "very disappointed," but a spokesman said Bush hoped the whole House would reject the bill.

The Armenian Assembly of America commended the move. "It is long past time for the U.S. government to acknowledge and affirm this horrible chapter of history," it said.

Similar resolutions have been introduced for years, with Armenian-American groups pressing for passage. But when Republicans ran Congress they blocked a floor vote. Now Democrats are in the majority and House Speaker Nancy Pelosi is a long-time supporter of such measures. Schiff has 225 co-sponsors, over half the House.

At the invitation of House leaders, the spiritual leader of Armenian Apostolic Christians worldwide, His Holiness Karekin II, gave the opening prayer in the House chamber on Wednesday morning, wearing the black-hooded attire of his church.

(Additional reporting by Caren Bohan, Matt Spetalnick)