The US Senate will hold a procedural vote Wednesday on a measure authorizing President Barack Obama to use military force against Syria.

Senate Majority Leader Harry Reid said Monday that the Senate will vote on a motion to debate the resolution endorsing "limited military action" in retaliation for Syria's alleged use of chemical weapons.

"This matter demands the attention of the Senate and this country (and) all should agree that we should have this debate," Reid said on the Senate floor as he ushered in the newest legislative session following a five-week summer recess.

Should there be objections to the motion, as at least one Republican senator threatened last week, the 100-member chamber would need 60 votes to move the resolution forward.

Obama's Democrats control the Senate, but it is unclear whether Obama has the necessary support in the upper chamber to meet the 60-vote threshold.

Two lawmakers -- first-term Democrat Heidi Heitkamp and veteran Republican Lamar Alexander -- announced Monday they would oppose the move to authorize the use of force.

"After step A, what will be steps B, C, D and E?" Alexander told his constituents in a speech early Monday.

"I see too much risk that the strike will do more harm than good by setting off a chain of consequences that could involve American fighting men and women in another long-term Middle East conflict."

The Senate resolution now being considered forbids US boots on the ground in Syria for combat purposes, but several war-weary lawmakers on both sides of the aisle have voiced concern that a strike on Syria would draw the United States deeper into a Mideast military entanglement.

Heitkamp said "there should be other ways, more appropriate to America's vital national security interests, to discourage and show our disgust with the Syrian government's apparent use of chemical weapons on its own people."

Heitkamp said she and Senator Joe Manchin, another Democrat who has voiced deep skepticism about Obama's plans, were drafting "an alternative approach" which would give Syrian President Bashar al-Assad 45 days to sign an international chemical weapons ban and start turning over such poison gas.

Meanwhile, about 100 anti-regime demonstrators, many of them of Syrian decent and waving pro-rebel flags, protested outside the US Capitol, urging Congress to vote 'yes' on authorization of the use of force.