The Senate has overwhelmingly approved a sweeping, £394 billion defence Bill, sending President Barack Obama a clear signal to move quickly to remove US combat troops from Afghanistan, tighten sanctions on Iran and limit his own authority in handling terror suspects.
Ignoring a veto threat, the Senate voted 98-0 for the legislation that authorises money for weapons, aircraft and ships and provides a 1.7% pay rise for the military.
After a decade of increasing Pentagon budgets, the vote came against the backdrop of significant reductions in projected military spending and the threat of deeper cuts from the looming "fiscal cliff" of automatic spending cuts and tax increases.
The Bill reflects America's war-weariness after more than a decade of fighting in Afghanistan, the messy uncertainty about new threats to US security and Washington belt-tightening in times of trillion-dollar-plus deficits.
Spending solely on the base defence budget has nearly doubled in the past 10 years, but the latest blueprint reins in the projected growth in military dollars. The Bill would provide some 526 billion dollars for the base defence budget, 17 billion for defence programmes in the Energy Department and about 88 billion for the war in Afghanistan.
House of Representatives and Senate negotiators must reconcile their competing versions of the Bill in the next few weeks.
Republican senator John McCain, who has pushed for greater US military involvement to end the civil war, sponsored the amendment. Mr Obama warned Syrian president Bashar Assad on Monday not to use chemical and/or biological weapons against his people as the US and its allies consider military options. "If military action has to be taken to prevent sarin gas to be used, Congress has to be involved," Mr McCain said.
But Republican senator Rand Paul, said it was a "bad idea to discuss contingency plans for war".
Last year Mr Obama and congressional Republicans agreed on nearly 500 billion dollars in defence cuts over 10 years. If the two sides fail in the next month to avert the "fiscal cliff" the Pentagon would face an additional 55 billion dollars in automatic, across-the-board cuts after the first of the year.