The senior Democrat on the U.S. House of Representatives Foreign Affairs Committee is pushing President Barack Obama's administration to train and arm some Syrian rebels, in addition to providing humanitarian assistance.
Representative Eliot Engel will introduce a bill on Monday that would authorize Washington to provide assistance "including limited lethal equipment" to carefully vetted members of the Syrian opposition, aides and activists aware of Engel's plans said on Sunday.
Washington has pledged non-lethal aid to Syria's rebels, but Obama has so far refused to give them arms, arguing that it is difficult to prevent the weapons from falling into the hands of militants who could use them against Western targets.
The push by Engel, a New York Democrat, which comes days before Obama is due to visit the Middle East, could strengthen the resolve of some U.S. legislators to do more to end the bloodshed in Syria.
A handful of Republican legislators, including Senators John McCain and Marco Rubio, have been pressing for various forms of U.S. military aid to the rebels.
The European Union also has been debating what aid is appropriate for the Syrian opposition. Other EU governments rebuffed efforts by France and Britain on Friday to lift an arms embargo to help opponents of Syrian President Bashar al-Assad, although they asked foreign ministers to discuss it again this week.
Engel sent a "Dear Colleague" letter on Friday to members of the foreign affairs committee seeking support for the bill and citing the estimated 70,000 Syrians who have died, 1 million refugees and 2.5 million people internally displaced since the rebellion against Assad began two years ago.
"It is time for us to develop a comprehensive approach to stopping the carnage," Engel said in the letter.
Although he acknowledged there are risks to arming the rebels, Engel said providing military aid to Syria's opposition would bring the humanitarian disaster to an end and help ensure that the United States has a constructive relationship with Syria's new government after the end of Assad's rule.
Engel's legislation would also authorize the administration to increase humanitarian assistance to Syrians affected by the two-year-long civil war and begin planning for the country's future after Assad.
Backing the Syrian opposition is increasingly seen as the only leverage that foreign powers have in trying to support the uprising against Assad.