The Oscar winner, who returned Monday from a five-day trip to the region, told a packed room at the National Press Club that he wants to use his "credit card" as a Hollywood star to highlight the plight of two million desperate refugees.
He won the Academy Award for best supporting actor this year for his role in the politically charged thriller "Syriana."
"Is the American government slow to act? Of course we're slow to act, we always are," Clooney said, referring to prior U.S. intervention in Rwanda and the Balkans.
"It's something that has to start today," Clooney said. "If we don't get to work on it today, there's a few thousand people who will be dead by the end of the week."
Traveling with a cameraman, Clooney and his father, Nick — a former television anchorman — documented horrible conditions in Sudanese refugee camps. He showed video excerpts of their interviews with families who said militias murder civilians, rape women and lay waste to villages.
"What we cannot do is turn our heads and look away and hope that this will somehow disappear," he said. "If we do, it will disappear and an entire generation will be gone and then only history will be left to judge us."
Clooney and his father plan to attend a Darfur rally Sunday on the National Mall in Washington. Rallies also are planned this weekend in more than a dozen other cities.
Clooney, who turns 45 next week, was joined Thursday by Sens. Sam Brownback, R-Kan., and Barack Obama, D-Ill., co-sponsors of a measure in Congress that would boost funds for peacekeeping and humanitarian aid to Darfur.
The lawmakers — far apart on many political issues — thanked Clooney for his efforts and called on the Bush administration to appoint a special envoy to the region. They also want a U.N. protection force mobilized to protect refugees.
"By you going, you draw attention and we get this," Brownback told Clooney, pointing to the throngs of reporters crammed in the Press Club meeting room.
The United States has authorized more than $300 million to help victims of violence and support peace talks in Sudan. President Bush has said he favors an expanded international role in Darfur, backing a larger security force and NATO involvement.
The conflict began in 2003, when rebels of ethnic African tribes took up arms against the Arab-dominated government, complaining of discrimination and mistreatment. The government responded with a brutal counterinsurgency led by Arab militias, known as the Janjaweed. At least 180,000 people have died, mainly of hunger and disease, and two million are homeless.