The Barack Obama administration is preparing to appoint a "full-time, high-level" envoy to address the conflict in Darfur, according to the actor George Clooney, who met the president and Joe Biden in Washington on Monday to lobby them on the issue.

Clooney said Obama and the vice-president had told him the envoy would report directly to the White House, and would be appointed following a foreign policy review currently taking place "at the senior-most levels". "They assured me, and wanted to assure the rest – whoever else is listening – this is high on their agenda," he said. "This is a huge policy step for us."

Clooney has campaigned for several years for greater US activism to end the conflict between rebels and Sudanese authorities in Darfur, which may have claimed 300,000 lives and displaced 2.7 million people, according to United Nations estimates. The international criminal court is due to decide next week whether to issue an arrest warrant for the Sudanese president, Omar al-Bashir, on war crimes charges.

"This isn't about needing American dollars. I understand that it's a very difficult time," Clooney said after his scheduled meeting with Biden and a separate, impromptu encounter with Obama. "It's not about needing American troops. It's about needing what we do best – what we have done best since the start of this country – which is good, robust diplomacy all across the world."

The actor, who missed Sunday night's Oscars ceremony for his White House appointment, is a UN messenger for peace, although this did not prevent the UN from revoking his security escort on a visit this month to eastern Chad, where he was touring refugee camps in the company of the New York Times columnist Nicholas Kristof. "If the UN is too craven to protect its own goodwill ambassadors – because they might criticise genocide – it's not surprising that it and the international community fail to protect hundreds of thousands of voiceless Darfuris," Kristof wrote.

Elizabeth Alexander, a Biden spokeswoman, said: "The vice-president informed Mr Clooney about the administration's ongoing review of Sudan policy and welcomed his observations from his trip, [and] thanked Mr Clooney for his work on this issue, which he believes is an important contribution to the public's understanding of the conflict in Darfur."

The actor brought with him to the White House 250,000 postcards signed by Americans urging more US action on Darfur. "I think somehow we should all know that these people are hanging on by the skin of their teeth," he told CNN.