* S&P 500 has struggled to close over 100-day moving average
* Energy to be in focus with Syria situation uncertain
* H&R Block down after results, car makers up on Aug sales
* Indexes up: Dow 0.2 pct, S&P 0.3 pct, Nasdaq 0.5 pct
By Ryan Vlastelica
NEW YORK, Sept 4 (Reuters) - U.S. stocks rose on Wednesday, as a rally in technology shares lifted the Nasdaq, though investors remained focused on whether there would be a Western-led military attack against Syria following a suspected chemical weapons attack on its civilians.
Energy has been the most volatile sector as investors bet a Middle East engagement would limit oil supplies. The question of whether there will be a U.S.-led military strike against Syria has been the market's primary driver over the past week. Crude fell 1.3 percent. Cabot Oil & Gas sank 1.8 percent to $39.23.
The Nasdaq was lifted by gains in large-cap tech companies. Micron Tech jumped 7.6 percent to $15.07 while SanDisk Corp added 4 percent to $57.50.
In company news, Ford Motor Co and General Motors both jumped more than 2.5 percent after reporting their August sales.
The S&P 500's 100-day moving average of 1,640.44 will be in view. The index is currently above that level, and surpassed it in each of the past four sessions, but hasn't closed above it since Aug. 26, a sign that near-term momentum continues to stall.
A clearer picture on a military move in Syria is expected after Congress votes on measures to authorize a strike in several days, though Secretary of State John Kerry said any resolution approving military force would prohibit "boots on the ground," comments that indicated that a strike would be limited in scope.
"We're waiting for the vote, and then to see what actually happens," said Mark Grant, managing director at Southwest Securities in Fort Lauderdale. "People hope there will just be a tactical strike and that's it. But there are worries about retaliation and a wider conflict isn't priced into the market."
The Dow Jones industrial average was up 27.17 points, or 0.18 percent, at 14,861.13. The Standard & Poor's 500 Index was up 5.59 points, or 0.34 percent, at 1,645.36. The Nasdaq Composite Index was up 16.64 points, or 0.46 percent, at 3,629.25.
Rochester Medical Inc jumped 44 percent to $19.87 after C.R. Bard Inc agreed to buy the company for $262 million.
Dollar General Corp shares rose 3 percent to $55.48 after reporting results that topped expectations.
H&R Block Inc reported an adjusted quarterly loss Tuesday that was wider than expected, sending shares down 3.2 percent to $27. SAIC Inc fell 7.5 percent to $14.01 after its results. The two companies marked the S&P's two biggest percentage decliners.
Hain Celestial Group Inc fell 3 percent to $79.42 a day after the company said activist investor Carl Icahn and his entities were cutting their stake in the company by roughly half.
Data showed the U.S. trade deficit widened slightly more than expected in July as exports dipped, but a rebound in imports pointed to some firming in underlying demand early in the third quarter.
Investors await the release of the U.S. Federal Reserve's Beige Book summary of economic conditions at 2:00 p.m. The report will be scoured for insight into when the central bank will begin to slow its accommodative monetary policies, which have fueled the equity market's gains in 2013.