US STOCKS-Wall St jumps for 2nd day; automakers, tech gain

* S&P 500 on track to close over 100-day moving average

* Automakers up on Aug sales

* Tech, financials also lead gains; Ciena shares jump on forecast

* Indexes up: Dow 0.8 pct, S&P 0.9 pct, Nasdaq 1 pct

By Caroline Valetkevitch

NEW YORK, Sept 4 (Reuters) - U.S. stocks jumped for a second day on Wednesday, retracing most of last week's Syria-related losses as the strongest monthly U.S. auto sales figures in almost six years added to optimism about the economy.

Financials and technology led gains on the S&P 500 along with the consumer discretionary sector, with shares of Ciena jumping 13.5 percent to $23.48 on four times its average daily volume after an upbeat revenue forecast. Shares of Juniper Networks (NYSE: JNPR - news) rose 5.8 percent to $20.57, while shares of Cisco gained 1.6 percent to $23.85.

Insurers also climbed, including Hartford Financial, up 1.8 percent at $30.75.

The auto data follows upbeat U.S. economic data on Monday, including that the U.S. manufacturing sector grew last month at its fastest pace in more than two years, which helped to support the view the Federal Reserve may soon slow its stimulus program.

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 auto sales data pointed to the industry's 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.

The S&P 500 is up 1.3 percent for the week so far after a loss of 1.8 percent last week, which was tied largely to worries over Syria. The index is on track to close above its 100-day moving average for the first time since Aug. 26.

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 U.S. military move in Syria is expected after Congress votes on measures to authorize a strike in several days, though top Republicans on Monday voiced support for U.S. President Barack Obama's call for military strikes against the country.

The Dow Jones industrial average was up 117.76 points, or 0.79 percent, at 14,951.72. The Standard & Poor's 500 Index was up 15.39 points, or 0.94 percent, at 1,655.16. The Nasdaq Composite Index was up 36.94 points, or 1.02 percent, at 3,649.55.

The S&P 500 has surpassed its 100-day moving average in each of the past four sessions, but hasn't closed above it.

"I would expect that most indices would probably breach the (100-day moving averages) in the short term," said Bruce Zaro, chief technical strategist at Delta Global Asset Management in Boston.

Shares of Micron Tech and SanDisk Corp (NasdaqGS: SNDK - news) rose after a fire at a plant operated by rival SK Hynix (KSE: 000660.KS - news) . Micron was up 5.3 percent at $14.75 while shares of SanDisk were up 2.9 percent at $56.88.

Shares of Ford were up 3.7 percent at $16.95 while GM shares were up 4.7 percent at $35.75.

Among decliners, H&R Block Inc (NYSE: HRB - news) reported an adjusted quarterly loss Tuesday that was wider than expected, sending shares down 1 percent to $27.60.