Traders pause during a moment of silence to honor victims of the 9/11 attacks on the World Trade Center, on the floor of the New York Stock Exchange September 11, 2013. REUTERS/Lucas Jackson

By Ryan Vlastelica

NEW YORK (Reuters) - U.S. stocks closed higher on Wednesday, with the S&P 500 up for a seventh straight day, as geopolitical fears eased amid diplomatic efforts to allow Syria to surrender its chemical weapons, averting a U.S. military strike.

The Nasdaq composite index ended slightly lower on a sell-off of Apple shares.

Market nervousness abated as U.S. President Barack Obama, faced with resistance in polls and Congress, said a Russian offer to pressure Syria to place its chemical weapons under international control raised the chances of putting off a strike.

In a nationally televised speech on Tuesday night, the president asked congressional leaders to delay a vote on authorizing military force to give the diplomatic efforts a chance.

"The speech lessens some of the macro concerns out there, and as the worst-case scenario around Syria becomes more unlikely, investors are rotating back towards the market," said Eric Teal, chief investment officer at First Citizens Bancshares in Raleigh, North Carolina.

The S&P 500 has risen about 3.4 percent over the past seven sessions, its longest winning streak since July.

Wall Street showed resilience even as Apple Inc , the largest U.S. publicly traded company by market capitalization, slumped a day after it unveiled new iPhone models that disappointed investors who were hoping for a cheaper versions or a new product line.

The stock fell 5.4 percent to $467.71, extending a 2.3 percent decline in the previous session. The stock suffered its worst two-day performance since April 18, and its loss of nearly $23 billion in market capitalization is roughly the total size of Dell .

Apple's announcement "was less than expected from a company that has a reputation for surprising with a killer product or strategy," said Mark Luschini, chief investment strategist at Janney Montgomery Scott in Philadelphia, which manages about $58 billion in assets.

The Dow Jones industrial average <.DJI> was up 135.16 points, or 0.89 percent, at 15,326.22. The Standard & Poor's 500 Index <.SPX> was up 5.11 points, or 0.30 percent, at 1,689.10. The Nasdaq Composite Index <.IXIC> was down 4.01 points, or 0.11 percent, at 3,725.01.

Traders looked ahead to the Fed's two-day policy meeting on September 17-18 when a decision is expected to begin to wind down $85 billion a month in bond purchases. That stimulus has been key in buoying the economy and boosting the benchmark S&P 500 index by nearly 18 percent so far this year.

Volume was light, with about 5.63 billion shares changing hands on the New York Stock Exchange, the Nasdaq and NYSE MKT, below the daily average so far this year of about 6.25 billion shares. About 53 percent of stocks traded on the New York Stock Exchange closed higher, while about half of Nasdaq-listed shares ended lower.

Housing stocks <.HGX> were strong performers, up 1.2 percent. D.R. Horton Inc jumped 3.2 percent to $19.50.

IBM rose 2.2 percent to $190.70 to lead gains on the Dow industrials a day after hardware distributor Synnex Corp said it will buy IBM's customer-care outsourcing business for $505 million. Synnex jumped 20 percent to $57.60.

Texas Instruments fell 0.7 percent to $40.03 after the No. 3 U.S. chipmaker lowered its third-quarter forecast.

Economic data showed wholesale inventories for July edged up 0.1 percent, less than an expected rise of 0.3 percent, but better than June's 0.2 percent decline.

Harvest Natural Resources Inc surged 26.5 percent to $5.25 after the oil and gas producer said it was in exclusive talks to sell itself to Argentina's Pluspetrol in a deal valued at about $373 million including debt.

U.S. Treasuries prices rose, with the benchmark 10-year U.S. Treasury note up 15/32, and the yield at 2.9103 percent.

(Editing by Nick Zieminski and Kenneth Barry)