* Fed's Williams sees QE3 expansion next year
* Caterpillar latest bellwether to cut guidance
* Paychex profit beats expectations, Red Hat disappoints
* Futures: Dow up 5 pts, S&P up 0.4 pt, Nasdaq down 0.5 pt
By Ryan Vlastelica
NEW YORK, Sept 25 U.S. stock index futures were little changed on Tuesday as a pessimistic outlook from Caterpillar Inc., the latest U.S. heavyweight to say the slowing global economy was hurting profits, was offset by hopes of more monetary stimulus.
* Equities have rallied in recent months on expectations for stimulus from central banks around the world, and announcements of easing earlier this month from the Federal Reserve and European Central Bank have kept the S&P 500 near multi-year highs.
* San Francisco Fed president John Williams said on Monday he expected the central bank to expand its bond-buying program next year to more aggressively combat the unemployment rate. He also expects the program to end before the close of 2014.
* Just minutes before markets closed on Monday, Caterpillar Inc cut its 2015 profit outlook, warning that weaker commodity prices would result in a bigger-than-expected fall-off in demand. Thee Dow component, however, stopped short of forecasting a global recession. Shares fell 2.2 percent to $88.87 in premarket trading.
* While central bank actions have kept equity gains largely intact, recent corporate outlooks have given investors a reason to be cautious about future growth. FedEx Corp and Norfolk Southern were among the companies that lowered their forecasts recently.
* S&P 500 futures fell 0.4 point but remained above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures added 5 points and Nasdaq 100 futures fell 0.5 point.
* The S&P 500 is on track for a 7.6 percent gain for the quarter, a rally largely tied to central banks' actions to stimulate their economies. After those gains, many market participants are looking for new catalysts to keep pushing shares higher.
* Analysts said investors are probably now participating in "window dressing," where fund managers add some of the latest outperformers to their portfolio.
* Paychex Inc reported a first-quarter profit that narrowly beat estimates, helped by higher revenue from its human resource services business.
* Red Hat Inc reported a lower-than-expected adjusted profit as costs rose, and lowered the top end of its full-year revenue outlook on slow growth in its services business.
* U.S. stocks closed flat on Monday as an index of German business sentiment declined for a fifth consecutive month in September, showing Europe's strongest economy was moving closer toward recession as the euro zone's debt crisis remains unresolved. Caterpillar's outlook further pressured sentiment going into the close.