[Updated at 9:44 p.m. ET] Referring to the Obama administration's contention that Standard & Poor's analysis of the government's finances was off by about $2 trillion, a Treasury Department spokesperson said: "A judgment flawed by a $2 trillion error speaks for itself."

The Standard & Poor's rating agency announced Friday evening that it has downgraded the U.S. credit rating to AA+ from its top rank of AAA.

On Friday afternoon, hours before S&P publicly announced the downgrade, the agency revealed its plans to the Obama administration and sent an analysis to the Treasury Department. The senior administration official said the analysis inflated U.S. deficits by $2 trillion.

Treasury analysts contacted S&P and challenged the analysis, and S&P acknowledged the mistake, the official said. But S&P said it still would stick with its decision to downgrade the United States' credit rating, according to the official.

"This is a facts-be-damned decision," the senior official said. "Their analysis was way off, but they wouldn't budge."

The official the administration can do nothing now but hope that S&P's decision and analysis faces outside scrutiny.

"These guys make Congress look good," the official said of S&P.

[Updated at 8:59 p.m. ET] Credit rating agency Standard & Poor's on Friday downgraded the credit rating of the United States, stripping the world's largest economy of its prized AAA status.

In July, S&P placed the United States' rating on "CreditWatch with negative implications" as the debt ceiling debate devolved into partisan bickering.

To avoid a downgrade, S&P said the United States needed to not only raise the debt ceiling, but also develop a "credible" plan to tackle the nation's long-term debt.

In its report Friday, S&P ruled that the U.S. fell short: "The downgrade reflects our opinion that the ... 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 also cited dysfunctional policymaking in Washington as a factor in the downgrade. "The effectiveness, stability, and predictability of American policymaking and political institutions have weakened at a time of ongoing fiscal and economic challenges."

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[Initial post, 7:15 p.m.] The Standard & Poor's rating agency served the Obama administration with notice Friday afternoon that it planned to downgrade the U.S. government's AAA credit rating, an administration official told CNN.

But S&P has yet to make its ruling public, and the source told CNN the agency is reconsidering after the administration challenged S&P's analysis of the government's finances.

The source, a senior official involved in the discussions, said the agency was off by "trillions" in its economic model and was now working to revise its analysis.

S&P did not return repeated calls for comment.

The official described the talks as a "moving target" and said "it's clear some people there still want to go forward" and downgrade U.S. debt.

Rumors swirled for most of the day Friday that S&P was preparing to make its move. But even several hours after the market close, official notice had yet to materialize.