William Burns, the assistant secretary of state for Near Eastern affairs, confirmed the move to a committee in the House of Representatives on Wednesday.
He said: "I think you'll see the implementation very shortly, and I think it will be a very firm implementation of the Syrian Accountability Act and the intent behind it."
Lawmakers have pressured President George Bush since November to impose penalties on Syria, which Washington also accuses of occupying Lebanon and failing to secure its border with Iraq while allowing anti-American fighters to make their way there.
US anti-Syria legislation has barred trade in items that could be used in weapons programmes until the administration certifies Syria is not supporting "terrorist" groups, has withdrawn personnel from Lebanon, is not developing weapons of mass destruction, and has secured its border with Iraq.
The legislation also includes barring US businesses from investing in Syria, restricting travel in the United States by Syrian diplomats, and banning exports of US products other than food and medicine to Syria.
A senior administration official said it was "probably accurate" that a decision on the sanctions was imminent. But he said: "We don't know when or what they will be."
Syrian President Bashar al-Assad
says US accusations are untrue
The official said what type of sanctions will be imposed was "being evaluated by the administration as we speak".
Burns was testifying to the House International Relations Committee on developments in Libya, which has renounced "terrorism" and is cooperating to dismantle its own weapons of mass destruction programme.
Asked if he has seen any similar moves in Syria, Burns said, "No sir".
Defense Secretary Donald Rumsfeld has repeatedly accused Syria and Iran of allowing "terrorists" to cross their borders into neighboring Iraq, and suggested during a visit to Iraq last month that it might be time for Washington to increase diplomatic and financial pressure on Damascus and Tehran.
Rumsfeld also says Syria and Iran have conspired to aid the movement of Hizb Allah fighters and arms through Lebanon to launch attacks against Israel.
Both Syria and Iran deny the charges and say they are politically-motivated.