Higher energy costs and a declining euro helped cause the slowdown.
"Analysts have really started slashing third-quarter numbers," Chuck Hill, director of research at First Call/Thomson Financial, said Wednesday. Companies often try to damp profit expectations, so per-share growth for the Standard & Poor's 500 Index may reach 19 percent, he said.
Eastman Kodak Co., DuPont Co., Whirlpool Corp. and TRW Inc. are among 270 companies that have already told shareholders that profits would be disappointing, compared with 180 in the second quarter, according to Bloomberg data.
Sales at Intel Corp., Oracle Corp. and Priceline.com Inc. were discouraging, a sign that quarterly profits may be sluggish.
Oil prices have tripled in the past 21 months to more than $31 a barrel, increasing costs at companies ranging from UAL Corp.'s United Airlines to aluminum maker Alcoa Inc.
The euro lost a quarter of its value in that time, eroding profits at Procter & Gamble Co. and others that get a significant part of their sales from Europe.
With energy prices remaining high and the euro unlikely to rebound, "the trend is definitely a diminishing growth rate," said Cummins Catherwood, a managing director at Rutherford, Brown & Catherwood Inc., which oversees $800 million in assets.
A slowing of the U.S. economy's nine-year expansion, after a series of interest-rate increases by the Federal Reserve, also may hurt profits.
The economy will increase by 3 percent in the third quarter, compared with 5.3 percent in the prior three months and 4.8 percent in the first quarter, according to a Bloomberg survey of economists.
Fourth-quarter profit growth may slow to 16 percent from 21 percent in the year-earlier period, said First Call, which collects estimates.
"There are some red flags looking into 2001," said Franklin Morton, director of research at Chicago-based Ariel Capital Management, which oversees $3.5 billion in assets.
Some companies are benefiting from the boost in oil prices. Projected per-share profit growth for energy producers has jumped to 90 percent from 29 percent since April.
Shares in oil exploration and production companies have risen by about 57 percent in the past six months.
Irving-based Exxon Mobil Corp., the largest public oil company, is likely to report an 84 percent increase in earnings, analysts said. Profit at Chevron Corp., the No. 2 U.S. oil company, will increase by three-quarters.
Natural gas prices, which have more than doubled this year, caused earnings to surge at exploration company Burlington Resources Inc.