The US secretary of state is seeking new funds for a policy aimed at putting pressure on Iran's government and promoting internal opposition to it.
Condoleezza Rice asked Congress for $75m to increase TV and radio broadcasts and fund dissident groups.
Correspondents say the move comes amid US fears that the world community will not countenance tough action over Iran's nuclear ambitions.
Critics of the US plan say the funds are not enough to make a difference.
Former Clinton administration official Martin Indyk told the Washington Post newspaper that the groups the US wants to fund have little support on the ground and have been unable to challenge the Islamic government in Iran.
Ms Rice is planning to visit the Middle East next week to discuss the Iranian issue with regional leaders.