WASHINGTON -- The United States lost its top-notch AAA credit rating from Standard & Poor's Friday, in a dramatic reversal of fortune for the world's largest economy.
S&P cut the long-term U.S. credit rating by one notch to AA-plus. The credit agency said late Friday that it was making the move because the deficit reduction plan passed by Congress on Tuesday did not go far enough to stabilize the country's
U.S. Treasuries, once undisputedly the safest investment in the world, are now rated lower than bonds issued by countries such as the United Kingdom, Germany, France or Canada.
The move is likely to raise borrowing costs eventually for the American government, companies and consumers.
"The downgrade reflects our opinion that the fiscal consolidation plan that Congress and the administration recently agreed to falls short of what, in our view, would be necessary to stabilize the government's medium-term debt dynamics," S&P said in a statement.
The decision follows a bitter political battle in Congress over cutting spending and raising taxes to reduce the government's debt burden and allow its statutory borrowing limit to be raised.
On Tuesday, President Barack Obama signed legislation designed to reduce the fiscal deficit by $2.1 trillion over 10 years. But that was well short of the $4 trillion in savings S&P had called for as a good "down payment" on fixing America's finances.
The political gridlock in Washington and the failure to seriously address U.S. long-term fiscal problems came against the backdrop of slowing U.S. economic growth and led to the worst week in the U.S. stock market in two years. The S&P 500 stock index fell 10.8 percent in the past 10 trading days.
"When they finally dealt with the debt ceiling, they obviously kicked the can down the road, and the market did not need that. I thought at the time when they released it there would have been a downgrade," said William Larkin, fixed income portfolio manager at Cabot Money Management in Salem, Mass.
"I don't think it is a great shock. If it didn't happen now, I think it probably would have happened in a couple of months.
The outlook on the new U.S. credit rating is negative, S&P said, a sign that another downgrade is possible in the next 12 to 18 months.
U.S. government officials had been bracing for a downgrade.
CNBC's John Harwood reported that S&P told the federal government at 1:30 p.m. ET Friday that it was preparing to downgrade the country's rating. But Harwood reported that after U.S. officials pointed out an error in how S&P computed the ratio of U.S. debt to the gross domestic product, S&P decided to reconsider.
A source said S&P's calculations were off by "trillions," CNBC reported. A source familiar with the discussions said that the Obama administration believes S&P's analysis contained "deep and fundamental flaws."
The rating agencies have been under fire since the financial meltdown of 2008 because they often gave high ratings to bundles of mortgage-related securities that were risky and ultimately failed.
The impact of S&P's move was tempered by a decision from Moody's Investors Service earlier this week that confirmed, for now, the U.S. Aaa rating. Fitch Ratings said it is still reviewing the rating and will issue its opinion by the end of the month.
"It's not entirely unexpected. I believe it has already been partly priced into the dollar. We expect some further pressure on the U.S. dollar, but a sharp sell-off is in our view unlikely," said Vassili Serebriakov, currency strategist at Wells Fargo in New York.
"One of the reasons we don't really think foreign investors will start selling U.S. Treasuries aggressively is because there are still few alternatives to the U.S. Treasury market in terms of depth and liquidity," Serebriakov added.
S&P's move is also likely to concern foreign creditors especially China, which holds more than $1 trillion of U.S. debt. Beijing has repeatedly urged Washington to protect its U.S. dollar investments by addressing its budget problem.
The downgrade could add up to 0.7 of a percentage point to U.S. Treasuries' yields over time, increasing funding costs for public debt by some $100 billion, according to SIFMA, a U.S. securities industry trade group.
S&P had placed the U.S. credit rating on review for a possible downgrade on July 14 on concerns that Congress was not adequately addressing the government fiscal deficit of about $1.4 trillion this year, or about 9.0 percent of gross domestic product, one of the highest since World War II.
The unprecedented downgrade of the nation's AAA credit rating by a major ratings agency comes only 15 months before the next presidential election where the downgrade and the debt will be top issues for debate.
Bitter political battles remain over the ideologically fraught issues of spending cuts and tax reform.
The compromise reached by Republicans and Democrats this week calls for the creation of a bipartisan congressional committee to find $1.5 trillion of deficit cuts by late November, beyond the $917 billion already identified.
Reuters and CNBC contributed to this report.