* U.S. durable good orders, home sales data on tap
* S&P downgrades Ireland; Japanese stocks hit 16-month low
* Futures down: Dow 18 pts, S&P 2.5 pts, Nasdaq 5.75 pts
* For up-to-the-minute market news see [STXNEWS/US]
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By Ryan Vlastelica
NEW YORK, Aug 25 (Reuters) - U.S. stock index futures fell on Wednesday as weakness in equities markets overseas kept traders cautious ahead of upcoming U.S. data on durable goods orders and home sales.
New home sales for July will be released at 10 a.m. [1400 GMT], and economists in a Reuters survey expect no change from the 330,000 unit annual rate in June. A revival of the housing market is considered crucial for an economic recovery, and on Tuesday, weak existing home sales data sparked a sell-off that sent stocks to seven-week lows.
"Home sales are driving the market right now, and yesterday's read doesn't bode well for today's data," said Cort Gwon, director of trading strategies at FBN Securities in New York. "A lot of weakness is discounted, but there's still downside potential if we miss (expectations)."
Data on July durable goods orders, also due at 10 a.m., are expected to show a rise of 2.8 percent after a 1.2 percent drop in June.
Standard & Poor's late on Tuesday cut its credit rating on Ireland and assigned it a negative outlook, expecting the country to face substantially higher costs to support its ailing financial institutions. For details, see [ID:nLDE67O0YY]
Japanese stocks hit a 16-month closing low as disappointment spread over the lack of policy action by Japan to rein in the strong yen. Japan's finance minister sharpened his rhetoric on the yen's steep gains after the Nikkei newspaper reported Japan may consider selling the yen in solo intervention if speculators drive it up. [ID:nTOE65T00N]
S&P 500 futures
American International Group Inc
JDS Uniphase Corp
Luxury homebuilder Toll Brothers Inc
U.S.-listed shares of Potash Corp
The Dow and S&P 500 notched their fourth straight day of losses on Tuesday as the unexpectedly large drop in home sales ratcheted up concerns that the economic recovery is even weaker than feared.
(Editing by Padraic Cassidy)