By Karen Pierog
(Reuters) - S&P Global Ratings on Thursday warned of "severe and extraordinary" consequences for financial markets if the United States defaults on its debt, although it added it expects the U.S. Congress will ultimately address the debt ceiling in a timely manner.
"It would be unprecedented in modern times for an advanced G-7 country, like the U.S., to default on its sovereign debt," S&P said in a bulletin.
Joydeep Mukherji, credit analyst for the United States, warned that a default would prompt the credit rating agency to slash its rating for the country with the world's biggest economy to D, its lowest level.
Mukherji said S&P's action would be the same in the case of debt nonpayments by other countries and that even a default on a single U.S. Treasury bill, note, or bond would push the U.S. rating to the bottom of the scale.
"We don't think it's going to happen," he told Reuters. "That's why we have a AA-plus rating, the second highest on our scale."
In 2011, S&P downgraded the top rating of the United States by a notch to its current AA-plus level.
U.S. Treasury Secretary Janet Yellen has warned that the government could run out of cash by Oct. 18 if the debt ceiling is not raised or suspended, leading to its first-ever default. A two-year suspension of the debt ceiling expired in July and Democrats and Republicans in Congress remain at odds.
Mukherji said defaults in other countries usually result from economic and financial stresses, and that political factors were driving the debt ceiling debate in the United States, which has a recovering economy.
He added that given the U.S. dollar is the world's most important currency, a default would have a far reaching impact.
"No one knows what the impact is," he said. "We don't know, we don't want to know but it's going to be big."
S&P noted that during the last decade, Congress passed legislation to raise or suspend the debt limit five times during periods of political impasse.
The nation had top credit ratings with all three major credit rating agencies until S&P's August 2011 downgrade amid a previous round of political battles over debt, deficits, and the debt ceiling.
As for a potential government shutdown, S&P said it would not have a direct impact on creditworthiness.
Congress on Thursday passed a stopgap funding bill to avoid a shutdown this week.
(Reporting by Mehr Bedi in Bengaluru and Karen Pierog in Chicago; Editing by Shailesh Kuber and David Gregorio)