NEW YORK (AP) -- The Standard & Poor's ratings agency said Monday it's getting more optimistic about the U.S. economy. But investors just yawned.

Stocks budged higher when trading opened, shortly after the S&P agency raised its outlook for the U.S. government's debt rating and credited "the strengths of the economy." But the gains proved both modest and fickle, and the market spent most of the day flitting between small gains and losses.

At day's end, the Dow Jones industrial average and the S&P 500 were lower, but just barely. The Nasdaq composite was slightly higher. It was a marked change from Friday, when the Dow jumped 207 points.

Trading volume was light, with no major economic reports or company announcements. The 10 industry sectors in the S&P were split down the middle, with half rising and half falling.

Booz Allen Hamilton slid after a company employee said he had leaked information about secret government surveillance programs. The consulting company's stock dropped 46 cents, or 2.6 percent, to $17.54.

On Monday, S&P upgraded its outlook on the U.S. debt rating to "Stable" from "Negative." That doesn't restore the U.S. government's top-shelf credit rating, but it means that S&P is unlikely to cut the rating again in the near future.

S&P cited the Federal Reserve's willingness to keep interest rates low, meant to spur borrowing and spending, and its bond purchasing program, which is meant to encourage investors to buy stocks and other riskier assets.