Stocks were pummeled this morning by a rumor that Standard & Poor’s would downgrade the United States, making the announcement after the close of markets Friday. When asked about this, S&P’s John Piecuch gave me the standard (and poor) answer: “We do not comment on market rumors about our ratings.”

Okay, so they don’t. I do. And so does everybody’s favorite source, the anonymous federal official.

The financial types I talked to today didn’t put much stock in the rumor, and, indeed, stocks largely recovered from their earlier plummet in day of whiplash volatility.

The consensus view, so far as I can tell: A downgrade is coming — S&P said about $4 trillion in spending cuts were needed, and Congress couldn’t deliver that — but there’s no reason to think it will come this weekend. (Not to say it couldn’t.) (UPDATE: It did.) S&P put the United States on its negative watchlist on July 14, and its practice is to make a decision within 90 days of such a designation. With Moody’s and Fitch having reaffirmed the U.S. AAA, S&P may hesitate to stand out from the crowd, and the view inside the firm is that markets already have priced in the downgrade risk. So, what’s the hurry?

The credit agencies also are surely taking into account the fact that Europe’s crisis has left the United States with even lower borrowing costs, which makes the nation’s debt, swollen and grotesque as it is, slightly more manageable. That’s Tim Geithner’s argument, for what it’s worth. (Your call.)

Point to ponder: We know, more or less, how a downgrade will affect the U.S. government. We know less about how it will affect all of the financial institutions — banks, pensions, insurance companies — that hold lots of Treasuries, or the state and local governments and pension funds that hold them.