NEW YORK – The United States had its AAA credit rating downgraded for the first time Friday by Standard & Poor’s on concern that spending cuts agreed on by lawmakers to raise the nation’s borrowing limit won’t be enough to reduce record deficits.

S&P dropped the ranking one level to AA+, after warning on July 14 that it would reduce the rating in the absence of a “credible” plan to lower deficits even if the nation’s $14.3 trillion debt limit was lifted. The United States was awarded the top credit ranking by New York-based S&P in 1941. It kept the outlook at “negative.”

“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.

Demand for Treasuries has surged even with the specter of a downgrade as investors saw few alternatives to the traditional refuge during times of risk. The action could still hurt the U.S. economy over time by increasing the cost of mortgages, auto loans and other types of lending tied to the interest rates paid on Treasuries. JPMorgan Chase estimated that a downgrade would raise the nation’s borrowing costs by $100 billion a year.

“It’s a reflection of the fact that we haven’t done enough to get our fiscal house in order,” Anthony Valeri, market strategist in San Diego at LPL Financial, said in an interview before the downgrade. “Sovereign credit quality is going to remain under pressure for years to come.”

Moody’s Investors Service and Fitch Ratings affirmed their AAA credit ratings Tuesday, the day President Barack Obama signed a bill that ended the debt-ceiling impasse that pushed the Treasury to the edge of default. Moody’s and Fitch also said that downgrades were possible if lawmakers fail to enact debt reduction measures and the economy weakens.

The measure raised the nation’s debt ceiling until 2013 and threatens automatic spending cuts to enforce $2.4 trillion in spending reductions over the next 10 years.

S&P put the U.S. government on notice on April 18 that it risks losing its AAA rating unless lawmakers agree on a plan by 2013 to reduce budget deficits and the national debt. S&P indicated last month that anything less than $4 trillion in cuts would jeopardize the rating.

“A grand bargain of that nature would signal the seriousness of policymakers to address the fiscal situation in the U.S.,” John Chambers, chairman of S&P’s sovereign rating committee, said in a video interview distributed by the ratings firm on July 28.

Obama has said a rating cut may hurt the broader economy by increasing consumer borrowing costs tied to Treasury rates. An increase in Treasury yields of 50 basis points would reduce U.S. economic growth by about 0.4 percentage points, JPMorgan said in a report, citing Federal Reserve research and data.

“The hope is that we could keep Treasuries pure, limited to interest rate risk,” Mohamed El-Erian, chief executive and co-chief investment officer at Pacific Investment Management Co., said in a Bloomberg Television interview before the announcement. “The minute you start downgrading away from AAA, you take small steps toward credit risk and that is something any country would like to avoid.”

Investors from China to the United Kingdom are lending money to the U.S. government for a decade at the lowest rates of the year. For many of them, there are few alternatives outside the United States, no matter what its credit rating.

“Yields are low in the face of a downgrade because there is nowhere else for people to go if they don’t buy Treasuries because they want to be in safe dollar assets,” Carl Lantz, head of interest-rate strategy at Credit Suisse, one of 20 primary dealers that trade directly with the Federal Reserve, said before the announcement.

Ten-year Treasury yields fell to as low as 2.33 percent in New York, the least since October. The committee of bond dealers and investors that advises the U.S. Treasury said the dollar’s status as the world’s reserve currency “appears to be slipping” in quarterly feedback presented to the government Wednesday. The U.S. currency’s portion of global currency reserves dropped to 60.7 percent in the period that ended March 31, from a peak of 72.7 percent in 2001, International Monetary Fund data show.