Tech pressures Nasdaq in volatile trading

Traders work on the floor of the New York Stock Exchange, May 22, 2012.

NEW YORK (Reuters) - Stocks ended slightly higher in a third session marked by late-day swings, but the Nasdaq fell after NetApp gave a weak revenue forecast, casting doubt on the outlook for tech spending.

Major indexes were lower for much of the session, as investors found little reason to buy following three days of gains. In addition, economic figures suggested slowing demand in both Europe and the United States.

However, Wall Street reversed course late in the session and the S&P extended its gains to a fourth straight day.

Underscoring the vulnerability of U.S. companies to events in the euro zone, data storage company NetApp Inc (NTAP.O) on Wednesday forecast revenue below expectations, citing uncertainty in Europe. Its shares tumbled 12 percent to $28.82.

"It's incredibly difficult to know what's priced into markets or what fair value might be for stocks," said Andrew Milligan, global head of strategy for Standard Life Investments in Edinburgh.

"Equities might have a better value relative to other asset classes, but they're certainly not as cheap as chips. We're not besotted with them."

Dow component Hewlett-Packard (HPQ.N) rose 3.3 percent to $21.77. The company said on Wednesday it would lay off about 8 percent of its workforce in the next couple of years.

Greece's future in the euro zone remains a primary risk for stocks. At least half of euro zone governments, as well as banks and large companies, are making contingency plans in case Greece decides to leave.

"The risk-off trade is very much the order of the day, so long as the potential contagion effect remains," said Milligan. "We don't know what policies might be proposed to keep Greece in the EU, and how Greece might respond to them."

The Dow Jones industrial average .DJI was up 33.60 points, or 0.27 percent, at 12,529.75. The Standard & Poor's 500 Index .SPX was up 1.82 points, or 0.14 percent, at 1,320.68. The Nasdaq Composite Index .IXIC was down 10.74 points, or 0.38 percent, at 2,839.38.

The S&P is up 2 percent on the week, though the market has lately undergone late-day shifts that have erased both losses and gains, a sign of the markets' skittishness.

Demand for long-lasting U.S. manufactured goods rose less than expected in April while weekly jobless claims dipped modestly for the week ended May 19, government data showed.

The transportation sector edged up despite a rebound in oil prices. The rise was led by airlines after JPMorgan raised its price target on several carriers.

U.S. Airways (LCC.N) jumped 10.5 percent to $12.16, its highest since November 2010, and an index of airline stocks .XAL gained 3.3 percent. U.S. Airways shares have more than doubled in 2012, rising about 140 percent.

After the closing bell on Wednesday, electronic trader Knight Capital Group (KCG.N) said it suffered a pre-tax loss of $30 million to $35 million on the botched Nasdaq trading debut of social media giant Facebook (FB.O) and is demanding the exchange compensate that amount.

Knight Capital Group shares fell 0.5 percent at $12.38 and Facebook shares (FB.O) rose 2.3 percent to $32.72.

United Technologies Corp (UTX.N) ended 0.8 percent lower at $73.50 after the Dow component launched a $9.8 billion corporate bond sale.

About 56 percent of companies traded on the New York Stock Exchange ended higher while slightly more Nasdaq-listed firms ended higher.

Volume was light, with about 6.55 billion shares traded on the New York Stock Exchange, the American Stock Exchange and Nasdaq, below last year's daily average of 7.84 billion.