U.S. warned of possible downgrade

Lawmakers need to show progress in dealing with the country's long-term fiscal problems, Treasury Secretary Tim Geithner said Thursday. "We don't have much time."

NEW YORK (CNNMoney) -- Quit messing around.

U.S. lawmakers got another stern warning from a leading credit rating agency on Thursday that there is now a very real possibility that the country's top-notch credit rating could be downgraded in the next three months.

Standard & Poors said in a statement it was placing the United States' sovereign rating on "CreditWatch with negative implications."

"[O]wing to the dynamics of the political debate on the debt ceiling, there is at least a one-in-two likelihood that we could lower the long-term rating on the U.S. within the next 90 days," the agency said in a statement.

The action on Thursday follows a move in April when S&P changed its outlook on the U.S. AAA rating to "negative" because at the time it couldn't see how lawmakers would create a path to real debt reduction.

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Since then "the political debate about the U.S.' fiscal stance and the related issue of the U.S. government debt ceiling has, in our view, only become more entangled," the agency said.

"[W]e believe there is an increasing risk of a substantial policy stalemate enduring beyond any near-term agreement to raise the debt ceiling," S&P noted.

Indeed, other warnings from ratings agencies Moody's and Fitch in the interim spurred more rhetoric than action from politicians. Seven weeks' worth of talks between the parties led by Vice President Joe Biden broke down in June after House Majority Leader Eric Cantor left the negotiations.

And regular meetings at the White House between President Obama and Capitol Hill brass over the past two weeks have showed no signs of real progress. Obama will hold a press conference Friday to offer an update on the negotiations.

A downgrade of U.S. credit would mean interest rates on U.S. bonds would go up. And it could have ramifications across global markets because U.S. bonds are considered the world's safe haven investment.

The Treasury issued an immediate response to the news.

"Today's action by S&P restates what the Obama Administration has said for some time: That Congress must act expeditiously to avoid defaulting on the country's obligations and to enact a credible deficit reduction plan that commands bipartisan support," Treasury official Jeffrey Goldstein said. (Read: Republican stance on taxes a bust with public)

A downgrade could come for one of three reasons, S&P explained:

-- If Congress and the administration fail to come up with a "credible solution" to U.S. debt and show no signs of agreeing on one in the foreseeable future.

-- If the United States misses any scheduled debt service payments, in which case S&P would issue a "selective default" meaning a default has occurred on some bonds but not others.

-- If S&P concludes that the debt ceiling debate so bogs down that it calls into question policymakers' "willingness and ability to timely honor the U.S.' scheduled debt obligations."

Treasury started sending letters to Congress back in January urging them to raise the $14.3 trillion debt ceiling -- which is the U.S. legal borrowing limit

The Treasury takes in, on average, about $125 billion less than it has to pay out on a monthly basis. To make up the difference it issues U.S. bonds, and because of the country's sterling rating, it is able to do so at very low rates.

If Congress doesn't raise the debt ceiling by Aug. 2, the Treasury will no longer be able to pay all of the country's bills in full and on time without interruption.