American stocks climbed the most in three weeks, led by manufacturers and financial companies, after growth in exports helped the economy expand faster than estimated in the second quarter.

American International Group Inc., Caterpillar Inc., and AT&T Inc. rose more than 3% each and helped lead gains in nine of ten industry groups in the Standard & Poor’s 500 Index after the Commerce Department said gross domestic product grew at a 3.3% annual rate. Tiffany & Co., the world’s second-largest luxury jewelry retailer, jumped the most in three years on profit that topped analysts’ estimates. Energy shares erased an early advance, and consumer companies rallied, as oil prices slipped more than $2 a barrel following three days of gains.

“The bears ran away for the weekend,” Frederic Dickson, who helps oversee $23 billion as chief market strategist at D.A. Davidson & Co. in Lake Oswego, Oregon, told Bloomberg Radio. The GDP report “was a lift. We haven’t had much positive news and that provided it.”

The S&P 500 gained 19.02 points, or 1.5%, to 1,300.68, capping its biggest three-day advance in a month. The Dow Jones Industrial Average increased 212.67, or 1.9%, to 11,715.18. The Nasdaq Composite Index added 29.18 to 2,411.64. More than five stocks rose for each that fell on the New York Stock Exchange.

The S&P 500 extended its August gain to 2.6% and wiped out losses from earlier in the week as the GDP report showed businesses are weathering rising inflation and more than $500 billion in subprime-related bank losses. The government’s initial estimate of economic growth was 1.9% last month and economists in a Bloomberg survey on average projected 2.7%. The data follows an unexpected advance in durable goods orders that helped boost stocks yesterday.

The Dow average’s 3% gain so far in August makes it the third-best-performing stock measure in the world this month, in dollar terms, and the S&P 500’s advance is no. 4., according to data compiled by Bloomberg.

The largest American insurer, AIG, rose the most in three weeks, adding 7.6% to $21.51. The biggest maker of bulldozers, Caterpillar, increased 3.1% to $71.68. The top American phone company, AT&T, added 3.3% to $32.23. All 15 homebuilders in S&P indexes advanced, leading a group of the stocks to its second day of gains exceeding 5%.

“You’re getting stronger growth, and that is conceivably good for equities,” Alan Gayle, the Richmond, Virginia- based senior investment strategist at Ridgeworth Capital Management, which oversees about $70 billion, said. GDP growth above 3% “suggests that the economy is not as bad as a lot of the recent commentary has suggested,” he said.