The United States will be "running on fumes" if its debt limit is not raised by August 2, the White House said on Wednesday, as it sought to kill talk that this was not a real deadline to strike a deficit deal.

Some analysts figure that incoming tax receipts will allow the United States to stave off default for a week or more after its borrowing authority expires on Tuesday.

White House press secretary Jay Carney said that at midnight on August 2 the country will lose its authority to borrow for the first time, meaning there is no alternative for Democrats and Republicans other than to compromise over a deal to reduce the deficit and lift the debt ceiling.

"People keep paying their taxes. Revenue comes in. Money comes in. The problem is there is not enough money because we can no longer borrow money to pay all our bills. You're basically running on fumes," Carney told reporters. "It is a crisis situation."

Rating agencies warn they could downgrade the top-notch U.S. AAA credit rating if the United States misses debt payments or if it fails to take significant steps toward controlling the long-term budget deficit.

Carney said that if there is no deal by August 2, the failure of Congress to have acted would send shock waves through financial markets. "There will be assessments made by investors around the globe about what the heck is happening in Washington," he said.