Alcoa Inc , the largest U.S. aluminum producer, reported a first-quarter profit that beat estimates, but its revenue missed Wall Street's target and its shares dropped 3 percent in after-hours trading on Monday.

Revenue in the quarter rose 22 percent to $5.96 billion, helped by rising prices for aluminum and alumina -- the raw material for the metal -- but it lagged the Wall Street forecast of $6.08 billion.

Also, Alcoa's output of alumina, or aluminum oxide, used in the production of aluminum metal, dipped slightly in the first quarter to 4.0 million metric tons from 4.2 million in the fourth quarter of 2010.

The company's shares, which have risen almost 40 percent in the last six months, fell 3.4 percent to $17.17 in after-hours trading on the New York Stock Exchange.

Alcoa's had a big run, so I don't think you're going to see a lot of upside from this number, said Stephen Massocca, managing director at Wedbush Morgan in San Francisco.

What's really going to worry the market is top-line growth, said Alan Lancz, president of the Alan B. Lancz & Associates investment advisory firm in Toledo, Ohio.

They've really improved margins as much as they can, and if you don't get the top-line growth now or it doesn't meet expectations, that leaves the market vulnerable. (For a graphic on Alcoa's earnings click on http://r.reuters.com/sub98r)

Chairman and Chief Executive Officer Klaus Kleinfeld told Wall Street analysts the company still expected global aluminum demand to grow by 12 percent this year with some industrial sectors, such as heavy trucks, growing even more.

We expect the aerospace market to grow 7 percent in 2011 -- that's actually up 1 percent from our previous estimate, he said, adding it was driven by Boeing and Airbus having a production backlog of six years.

For the automotive sector, Kleinfeld said: If the recovery continues to be strong, we expect overall on a global basis growth between 5 percent to 11 percent.

For heavy trucks and trailers, Alcoa has increased its growth estimate to a range of 5 percent to 10 percent and for North America, Kleinfeld said he was projecting truck and trailer growth at the rate of 45 percent to 50 percent this year.

The beverage can segment, he said, was expected to be flat globally, while the weakest sector is still commercial building and construction, with moderate weakness in North America and Europe despite healthy growth in China.

In North America we expect further contraction of minus 4 percent to minus 8 percent. That pretty much shows that when it comes to commercial building and construction in North America, that's a pretty fragile market still.

In its earnings release, Alcoa said income from continuing operations, excluding special items, was 28 cents a share. That topped analysts' expectations of 27 cents a share, according to Thomson Reuters I/B/E/S.

Net first-quarter earnings were $308 million, or 27 cents per share, compared with a net loss of $201 million, or 20 cents per share in the same quarter of 2010, the Pittsburgh-based company said.

Alcoa said the improvement was driven by higher realized prices for aluminum and alumina.

The price of aluminum has climbed more than 30 percent in the past year, from around $1,990 per ton during the first quarter of 2010. On Monday, aluminum jumped to $2,720 a ton, a level last seen in August 2008, before ending down $24 at $2,689 a ton.

(Reporting by Steve James, editing by Bernard Orr)

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