* S&P 500 has struggled to close over 100-day moving average
* Energy to be in focus with Syria situation uncertain
* H&R Block posts wider-than-expected quarterly loss
* Indexes lower: Dow 11 pts, S&P 0.9 pt, Nasdaq 2 pts
By Ryan Vlastelica
NEW YORK, Sept 4 (Reuters) - U.S. stock index futures were flat on Wednesday as concerns grew that there would be a Western military strike against Syria, though any decision remains several days away.
* The odds for military action had appeared to ebb over the weekend after U.S. President Barack Obama said he would seek Congressional authorization for a strike. While there won't be a vote until Congress returns from its summer recess on Sept. 9, key congressional figures backed the plan, suggesting approval may be more likely.
* In addition, Russia signaled that it hadn't ruled out agreeing to military action if Damascus were proven to have carried out a chemical weapons attack.
* The geopolitical uncertainty has been the market's primary driver over the past week, with investors concerned about the economic impact of any action. Energy has been the most impacted, with crude rising 1.3 percent over the past two weeks as investors bet that a Middle East engagement would hurt oil supplies.
* Adding to the overseas uncertainty, Italian shares slumped on renewed uncertainty over the survival of the country's government. European shares lost 0.4 percent.
* S&P 500 futures fell 0.9 point and were even with 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 slid 11 points and Nasdaq 100 futures lost 2 points.
* On the S&P 500, investors will be watching the 1,639.88 level, the index's 100-day moving average. The index has risen above that level in each of the past four sessions, though it hasn't been able to close above it since Aug. 26, a sign that near-term momentum continues to stall.
* H&R Block Inc late Tuesday reported an adjusted quarterly loss that was wider than expected, citing higher costs.
* SAIC Inc and Dollar General Corp reported results early Wednesday.
* Hain Celestial Group Inc shares will be in focus a day after the company said that activist investor Carl Icahn and his entities were cutting their stake in the company by roughly half.
* While geopolitical issues have been the primary focus for investors, they will also be watching the latest economic data, with the July international trade figures out at 8:30 a.m. (1230 GMT).
* The U.S. Federal Reserve's Beige Book summary of economic conditions will be released at 2 p.m., and the report will be closely scoured for any insight into when the central bank may begin to slow its accommodative monetary policies, which have fueled the market's gains in 2013.
* Wall Street rose on Tuesday, but pared its gains in afternoon trading as key figures in Congress announced support for military action against Syria.