Armenian-Americans have lobbied for official use of the world "genocide"
The Obama administration has called on a Congressional panel not to describe the killing of Armenians by Turkish forces during World War I as genocide.
US Secretary of State Hillary Clinton urged the chairman of the House Foreign Affairs Committee to hold off a vote on the issue, the White House said.
She said the non-binding resolution would harm talks between Turkey and Armenia.
The resolution is fiercely opposed by Turkey, a key ally of the US.
In 2007, a similar resolution passed the committee stage, but was shelved before a House vote after pressure from the George W Bush administration.
Turkey has warned of consequences for US-Turkey ties if the latest resolution is passed.
During his election campaign President Barack Obama promised to brand the mass killings genocide.
On Thursday, committee chairman Howard Berman urged fellow members of the committee to endorse the resolution despite the White House warnings.
"I believe that Turkey values its relationship with the United States at least as much as we value our relations with Turkey," he said.
The Turks, he added, "fundamentally agree that the US-Turkish alliance is simply too important to get side-tracked by a non-binding resolution passed by the House of Representatives".
Even if the committee approves the resolution, it is unclear whether it will go forward to a vote in the House of Representatives.
A Turkish parliamentary delegation has gone to Washington to try to persuade committee members not to approve the resolution.
It calls on Mr Obama to ensure that US foreign policy reflects an understanding of the "genocide" and to label the World War I killings as such in his annual statement on the issue.
Nationalist sentiment is intense in Turkey and, if the resolution passes, there will be an emotional reaction, even by those who have been arguing for reconciliation with Armenia, says the BBC's Jonathan Head in Istanbul.
In October last year, Turkey and Armenia signed a historic accord normalising relations between them after a century of hostility.
Armenia wants Turkey to recognise the killings as an act of genocide, but successive Turkish governments have refused to do so.
Hundreds of thousands of Armenians died in 1915, when they were deported en masse from eastern Anatolia by the Ottoman Empire. They were killed by troops or died from starvation and disease.
Armenians have campaigned for the killings to be recognised internationally as genocide - and more than 20 countries have done so.
Turkish officials accept that atrocities were committed but argue they were part of the war and that there was no systematic attempt to destroy the Christian Armenian people.