The resolution on Litvinenko, who died of radioactive polonium poisoning in London in November 2006, was proposed by Republican Congresswoman Ileana Ros Lehtinen and approved by the House of Representatives' foreign affairs committee. The House is expected to vote on the document on April 1.
The draft resolution calls on President George W. Bush and Secretary of State Condoleezza Rice to pressure Moscow to cooperate in investigating the Litvinenko case.
"The murder of Mr. Litvinenko, a political dissident who was forced into exile by the Russian Government, is cause for great alarm," Ros-Lehtinen said last week. "The Russian government should cooperate fully with British investigators and ensure the security of radioactive materials."
The Litvinenko Justice Foundation said in a statement released in London on Monday that Marina and Walter Litvinenko had sent letters to the leaders of the U.S. House and Senate saying the resolution is important for promoting "justice and security."
London has said Andrei Lugovoi poisoned Litvinenko, a fierce Kremlin critic, and has demanded his extradition from Russia. Moscow has refused to extradite the former Kremlin security guard-turned businessman, who is now a nationalist lawmaker, saying the evidence is insufficient. Lugovoi, who met with Litvinenko in London before he fell ill, denies any involvement and says Litvinenko tried to recruit him to the British Secret Intelligence Service (MI6).
The dispute has led to a dramatic deterioration in relations between London and Moscow, including tit-for-tat expulsions of diplomats and the closure of two British Council offices in Russia.