“We need a clear strategy that will not mire the United States in a bloody and uncertain war,” Udall said on the Senate floor Tuesday. “I remain unconvinced that we have such a strategy in place."

President Obama has asked for congressional support to use limited military strikes against Syrian President Bashar Assad, who is accused of using chemical weapons against his own people.

Last week, the Senate Foreign Relation Committee passed on a bipartisan 10-7 vote S.J.Res. 21, which would authorize a limited 60-day strike with the option to extend it an additional 30 days. Udall voted against that resolution.

“Lets be clear, this is a vote to authorize an act of war,” Udall said. “There are strong reasons not to do so — first we should pursue all diplomatic options.”

Obama will address the nation Tuesday evening as new possibilities about a negotiated settlement with Syria seem likely to slow congressional action. Lawmakers are now working on a new resolution that would authorize military action only if Syria refuses to relinquish its stockpile of chemical weapons to international control.

On Monday, Russia suggested an agreement under which Syria would give up control of its chemical weapons, and Syria indicated it could agree to this solution. That prompted Obama to acknowledge that this sort of agreement could allow Syria to dodge a U.S. attack.

Udall said he was encouraged by diplomatic proposals being considered and urged the president to keep pressure on Russia to follow through.

“This situation will not be solved with Tomahawk cruise missiles launched into Syria,” Udall said. “A military strike on Syria is the wrong response.”