* S&P coming off worst session since June
* Investors seek positive catalysts as Q3 nears end
* New home sales data on tap, seen rising modestly
* Futures down: Dow 5 pts, S&P 1.2 pt, Nasdaq 4.25 pts
By Ryan Vlastelica
NEW YORK, Sept 26 (Reuters) - U.S. stock index futures were flat on Wednesday as investors took a break from the previous day's sharp decline, which was the S&P's worst day since June.
* Market participants have been seeking new catalysts to keep pushing shares higher since the U.S. Federal Reserve and European Central Bank announced stimulus measures earlier this month. The S&P is up almost 6 percent so far this quarter, with much of those gains coming on expectations for such announcements from the central banks.
* Further gains may be hard to come by amid concerns over the impact that slowing global growth could have on companies. Tuesday's sell-off came as Caterpillar Inc became the latest high-profile company to cut its outlook, joining FedEx Corp.
* In another discouraging sign for corporate America, Jabil Circuit late Tuesday reported fourth-quarter earnings that missed expectations and forecast weak first-quarter results.
* S&P 500 futures fell 1.2 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 fell 5 points and Nasdaq 100 futures lost 4.25 points.
* The S&P 500 is up 2.5 percent so far in September, historically a difficult month for the market, and recently hit the highest level in nearly five years.
* The last session of the third quarter is Friday, and the quarter's strongest performers could see some additional upside on "window dressing," when money managers add the latest outperforming stocks to their portfolios before the end of the quarter. MetroPCS and Sprint Nextel are the top two gainers quarter-to-date.
* Yahoo Inc's new chief executive Marissa Mayer laid out broad goals for the Internet giant in her first companywide address Tuesday. The company also named a new chief financial officer.
* Investors are also looking ahead to August new home sales, due out at 10 a.m. (1400 GMT) Analysts expect 380,000 units sold in the month, up modestly from 372,000 in July.
* While the housing market has shown signs of strengthening, and homebuilders have reported strong results recently, the July Case-Shiller report on home prices, released on Tuesday, came in weaker than expected.
* U.S. stocks tumbled on Tuesday, pressured by Caterpillar's outlook and weakness in Apple Inc shares. It was the S&P 500's biggest percentage daily loss since June 25 and the biggest for the Nasdaq since July 20.