A key Senate committee could vote as early as Wednesday on a measure authorizing U.S. military action in Syria.
Leaders of the Foreign Relations Committee agreed late Tuesday on details of the plan that would give President Barack Obama authority to order limited strikes against Syrian military targets for 60 days. He could extend the window by another 30 days under certain conditions.
The resolution would not authorize the use of ground troops. It states military action must be aimed at deterring and preventing Syria from carrying out future chemical weapons attacks.
The measure would also require Mr. Obama to present a strategy for bringing a political resolution to the Syrian crisis.
The authorization must clear the committee and gain approval in the full Senate and House of Representatives before taking effect.
John Boehner and Nancy Pelosi, the Republican and Democratic leaders in the House, expressed their support for the president's plan on Tuesday. Others in Congress remain leery of approving military force.
Secretary of State John Kerry told the Foreign Relations Committee he has no doubt that U.S. inaction on Syria would lead to a greater war and more use of chemical weapons.
He said it is beyond any reasonable doubt that President Bashar al-Assad's government used chemical weapons on civilians in the attack last month that killed more than 1,400 people near Damascus. He said there is solid evidence the Syrian military carefully prepared for the attack.
Syria has denied using chemical weapons, alleging it was the rebels who deployed them.
Russian officials have said they are not convinced by evidence the United States has shared so far.
Russian President Vladimir Putin said late Tuesday that the U.S. should present "convincing" evidence to the United Nations. He said he "doesn't exclude" supporting a U.N. authorization of force against Syria if there is such proof, but warned the U.S. against taking action without U.N. approval.