Caterpillar Inc , the world's largest maker of construction and mining equipment, posted stronger-than-expected quarterly earnings on Wednesday and said it was seeing encouraging signs that economies around the world were rebounding.

But the company also forecast 2010 profit below the average Wall Street estimate, and its shares fell 2.9 percent in premarket trading.

Caterpillar updated its outlook for 2010, saying it now expects a profit of $2.50 a share on sales of $35.6 billion to $40.5 billion. Analysts' average earnings forecast was $2.71 a share, according to Thomson Reuters I/B/E/S.

Eli Lustgarten, an analyst at Longbow Securities, said the whisper number was probably closer to $3.00 a share

So they're offering a little more cautious outlook on profitability than some of the more optimistic analysts were hoping for, Lustgarten said.

Caterpillar said it expects the world economy to grow more than 3 percent in 2010, led by developing economies like China, which it said would grow more than 10 percent.

It warned that the United States, the world's largest economy, would grow just 3.5 percent, well below levels seen in past recoveries.

Caterpillar said a continued decline in nonresidential building construction, and delays in passing a highway bill, would likely will cause highway contractors to remain cautious about purchasing equipment.

It reported a fourth-quarter net profit of $232 million, or 36 cents a share, down from $661 million, or $1.08 a share, a year earlier.

Sales fell 39 percent to $7.9 billion.

Stripping out costs associated with the company's restructuring, which involved the elimination of nearly 25,000 jobs worldwide, Caterpillar said it earned 41 cents a share.

On that basis, analysts, on average, expected the Peoria, Illinois-based company to report a profit of 28 cents a share, on sales of $8.11 billion, according to Thomson Reuters I/B/E/S.

Caterpillar, which has described the downturn in its business in 2009 as the worst since the Great Depression, said it was seeing encouraging signs of a rebound in demand for its products.

We have seen a marked increase in demand for mining equipment -- a result of continued strong commodity prices and growing confidence in economic recovery, Jim Owens, the company's chairman and chief executive, said in a statement.

Owens said the company had also seen an increase in sales of aftermarket service parts, which he said is usually an early indicator of growing demand for machines and engines.

In premarket trading, Caterpillar shares were down $1.62 at $54.23.

(Reporting by James B. Kelleher; editing by John Wallace)