The resolution, which the Security Council approved Tuesday, removed harsh language in an effort to pick up votes.
Speaking before the U.N. action, Democratic Sen. Russ Feingold, who chairs the Senate Foreign Relations subcommittee on Africa, called it "welcome and overdue" that the Security Council was prepared to pass a resolution that would send a peacekeeping mission to protect the people of Darfur, where more than 200,000 people have died and 2.5 million have been displaced since 2003.
He added: "I am very disappointed that the resolution's co-sponsors have succumbed to pressure from the Sudanese government" and removed the threat of sanctions. One item deleted was the Chapter 7 clause, which deals with threats to international peace and can be militarily enforced.
Two other senators also said the resolution did not go far enough.
Sudan's government is accused of using a militia of Arab nomads known as the janjaweed to retaliate against a rebellion by ethnic African tribes. Sudan has denied the charge.
Feingold said he understood the need for diplomatic compromise, but said the resolution has been "unacceptably weakened." He said that under the resolution, the Sudanese government would evade its requirements without consequences.
"Should that happen, the toll of the genocide in Darfur will continue to mount, in lives lost and persons displaced and fundamental human values that the international community has failed to uphold," he said.
"It's the first time I've ever picked up the phone to call ambassadors from other countries about a vote in the United Nations Security Council, but I think it's that important," he said.
"Today's action by the U.N. is a start, but it is only a start," Durbin said. "There is more to be done, and it needs to be done now."
Sen. Robert Menendez, also a Democrat, said he was disappointed that the resolution had been "watered down."
"While I understand the need to negotiate a resolution that will pass, ultimately we cannot let this manipulation continue," he said. "We cannot let Sudan's ambassador have veto power over these lives. We cannot let nations with permanent seats and veto power on the council continue to act irresponsibly."