* Earnings expected to grow, but may struggle to top forecasts
* Alcoa rises after market close as earnings beat expectations
* Consumer staples lead the day's advance, Monster Beverage jumps
* Lufkin stock jumps almost 38 pct on GE's plan to buy company
* Dow up 0.3 pct, S&P 500 up 0.6 pct, Nasdaq up 0.6 pct
By Ryan Vlastelica
NEW YORK, April 8 (Reuters) - U.S. stocks ended a volatile session higher on Monday as investors looked ahead to an earnings season expected to show modest growth despite concerns about macroeconomic conditions.
Wall Street fluctuated between positive and negative territory for much of the day before climbing in the final hour of trading, ending near its session highs. However, volume was light and the Dow's gains were limited by a selloff of Johnson & Johnson shares.
Forecasts for first-quarter earnings have been scaled back in 2013, with profits seen rising just 1.6 percent from the year-ago quarter, according to Thomson Reuters data. In January, earnings were seen rising 4.3 percent.
The drop in expectations has come as economic figures suggest the recovery could be less robust than some had thought. Weak corporate results could give investors further reasons to sell, pushing both the Dow and the S&P 500 back from recent all-time closing highs.
"We're waiting for earnings for evidence that the market can be supported at these levels," said Jim Dunigan, chief investment officer at PNC Wealth Management in Philadelphia. "We will see growth in earnings, but clearing the expectations bar could be difficult, which could give us reason to pause."
The season unofficially started after the market closed with results from Alcoa Inc. The stock rose 1.3 percent to $8.50 in extended-hours trading after adjusted earnings topped expectations.
As the first Dow component to report, Alcoa is informally viewed as setting the initial tone for the season, though many more bellwether companies' earnings won't come out until next week. The S&P materials index ended Monday's session up 0.4 percent.
Among the day's most active names, Advanced Micro Devices jumped 13 percent to $2.59 as the S&P 500's biggest percentage gainer, while Monster Beverage rose 4.7 percent to $52.01, helping boost the S&P consumer staples sector index, which rose 1.1 percent.
On the downside, J&J fell 1.1 percent to $81.11 after JPMorgan downgraded the healthcare company's stock to "neutral" from "overweight," saying it faced "a messy first quarter and a likely downward revision to 2013 guidance."
The Dow Jones industrial average was up 48.15 points, or 0.33 percent, at 14,613.40. The Standard & Poor's 500 Index was up 9.76 points, or 0.63 percent, at 1,563.04. The Nasdaq Composite Index was up 18.39 points, or 0.57 percent, at 3,222.25.
Stocks have rallied strongly this year with major indexes hitting record highs, helped in part by the Federal Reserve's stimulus program. The S&P 500 is up 9.6 percent for the year so far, while the Dow has gained 11.5 percent.
Despite that, major indexes posted their worst weekly loss for 2013 last week, with the payroll report fueling concerns about economic growth.
"A lot of the momentum we had in the first quarter was based on improving economic news, and the jobs report really took the wind out of our sails," said Dunigan, who helps oversee $116 billion in assets. "We're still trying to sift through what that means for our prospects going forward."
Volume was light, with about 5.02 billion shares changing hands on the New York Stock Exchange, the Nasdaq and NYSE MKT, well below the daily average so far this year of about 6.48 billion shares.
Two-thirds of the stocks traded on the New York Stock Exchange closed in positive territory, while about 60 percent of Nasdaq-listed shares ended higher.
Loose monetary policy from central banks around the world is expected to keep equities attractive. Recently investors have been using market declines as buying opportunities.
The Bank of Japan started its bond purchases on Monday after it announced last week that it will inject about $1.4 trillion into the economy in less than two years.
Fed Chairman Ben Bernanke will give a speech later on Monday after markets are closed. Investors have been watching for any insight into the Fed's thinking on how long the central bank will keep its asset purchase program in place as it tries to boost the economic recovery.
General Electric Co said it will buy oilfield pump maker Lufkin Industries Inc for about $2.98 billion, driving Lufkin shares up 37.6 percent to $87.96. GE, a Dow component, rose 0.8 percent to $23.12.
The news lifted energy names, with WPX Energy Inc up 5.3 percent at $17.01.