* S&P coming off worst session since June
* Investors seek positive catalysts after monetary stimulus
* New home sales data on tap, seen rising modestly
* Futures down: Dow 5 pts, S&P 2.8 pt, Nasdaq 9.75 pts
By Ryan Vlastelica
NEW YORK, Sept 26 (Reuters) - U.S. stock index futures fell slightly on Wednesday a day after the S&P 500 index suffered its 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 this month. The S&P is up almost 6 percent so far this quarter, with much of the gain due to central banks.
But slowing global growth may make continued improvement in company profits hard to come by. Tuesday's selloff came as Caterpillar Inc became the latest high-profile company to cut its outlook, joining FedEx Corp.
"Buyers have reached a point of exhaustion after FedEx and Caterpillar and the like, all of whom pointed to economic weakness," said James Dailey, portfolio manager at TEAM Asset Strategy Fund in Harrisburg, Pennsylvania. "People had been buying on the idea that the Fed would prop everything up, but if they can't, there's real potential for panic selling."
In another discouraging sign, technology company Jabil Circuit late Tuesday reported fourth-quarter earnings that missed expectations and forecast weak first-quarter results. The stock was down 4.5 percent to $20.03 in premarket trading.
S&P 500 futures fell 2.8 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 9.75 points.
Investors are also looking ahead to August new home sales, due at 10 a.m. (1400 GMT) Analysts expect the report to show 380,000 units sold in the month, up modestly from 372,000 in July.
Weakness appeared in overseas markets as well. European shares slumped 1.5 percent as Spain's economy contracted in the third quarter and investors awaited the country's 2013 budget, to be released this week. Hong Kong shares lost 0.8 percent.
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.
"Lately, we've been at these levels because anytime there was a selloff like on Tuesday, we would buy on the dip," Dailey said. "If we continue to fall today, that would represent a very significant change in character for how we're responding to bad news."
The quarter's best performing stocks could be helped on Friday, the last session of the third quarter, by "window dressing" in which money managers add outperforming stocks to their portfolios. MetroPCS and Sprint Nextel are the top two S&P 500 gainers for the quarter to date.
Yahoo Inc new Chief Executive Marissa Mayer laid out broad goals for the Internet company in her first companywide address Tuesday and chose a new chief financial officer. Shares rose 0.6 percent in premarket trading.
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.