US STOCKS-Wall St jumps on gains in auto maker sales

* S&P 500 has struggled to close over 100-day moving average

* Auto makers up on Aug sales

* Tech, financials also lead gains

* Indexes up: Dow 0.7 pct, S&P 0.9 pct, Nasdaq 0.9 pct

By Caroline Valetkevitch

NEW YORK, Sept 4 (Reuters) - U.S. stocks jumped on Wednesday, led by gains in auto makers and technology shares after data showing U.S. auto sales made their strongest monthly gains since November (Xetra: A0Z24E - news) 2007.

Shares of Ford (NYSE: F - news) and General Motors (NYSE: GM - news) jumped after they reported sales that beat analysts' expectations, and an index of automakers was up 2.8 percent.

The industry was on pace for its strongest month since just before the start of the 2007-2009 recession.

"If these sales numbers are the best in six years, that points to an improving economy and that's helping the market," said Stephen Massocca, managing director at Wedbush Equity Management LLC in San Francisco.

Financials were also sharply higher, helped by gains in insurers. Shares of Hartford Financial were up 1.8 percent at $30.75.

The Nasdaq was lifted by gains in large-cap tech companies.

Micron Tech jumped 3.5 percent to $14.50 while SanDisk Corp (NasdaqGS: SNDK - news) added 2.1 percent to $56.48.

Investors remained focused on whether there would be a Western-led military attack against Syria following a suspected chemical weapons attack on its civilians.

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.

The Dow Jones industrial average was up 108.93 points, or 0.73 percent, at 14,942.89. The Standard & Poor's 500 Index was up 13.89 points, or 0.85 percent, at 1,653.66. The Nasdaq Composite Index was up 32.59 points, or 0.90 percent, at 3,645.20.

Shares of Ford were up 3.4 percent at $16.89 while GM shares were up 3.3 percent at $35.28.

Traders are watching the S&P 500's 100-day moving average of 1,640.44. 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.

Among decliners, H&R Block Inc (NYSE: HRB - news) reported an adjusted quarterly loss Tuesday that was wider than expected, sending shares down 3.2 percent to $27.