WASHINGTON- An attempt to impose new sanctions on Iran over its nuclear program has stalled in the US Congress and lawmakers are discussing whether to introduce a much weaker measure, congressional aides said on Monday.Members of the Senate and House of Representatives are considering a non-binding resolution that expresses concern about Iran's nuclear ambitions and calls for negotiators to set strict conditions in talks between Tehran and world powers.That would fall short of tightening sanctions on Iran, as envisioned in a bill that senators have been discussing for months."We don't think it is going to come to a vote," said a Senate aide who requested anonymity because that person was not authorized to speak to the media. "There are discussions about a resolution."Iran has warned that it will walk away from talks on its nuclear program - raising the risk of conflict in the Middle East - if Congress passes a new sanctions bill.Senate Democrats met recently and agreed not to push Majority Leader Harry Reid to bring the sanctions bill to the floor of the chamber, congressional aides said.President Barack Obama's administration strongly opposed the sanctions bill, and threatened to veto it. The bill was co-sponsored by 59 of the 100 senators, including 16 of Obama's fellow Democrats.