American Freightways Corp., the fastest growing carrier in the less-than- truckload industry, said Tuesday it will post third-quarter earnings significantly below analyst expectations.

The Harrison, Ark., carrier said its profit would be in the 7 to 11 cent a share range, down from earlier projections of 27 to 31 cents a share. In the third quarter of 1994, it had a profit of 24 cents a share.The news follows similar announcements last week by some other trucking companies, and suggests that trouble throughout most of the industry in the second quarter is continuing into the third quarter.

American Freightways results were partly due to expansion into five new states in July and August. The expansion plans were due, however, to soft freight levels. The company decided to use excess equipment to start serving Florida, Colorado, Wisconsin, Nebraska and part of Minnesota, states it originally did not plan to enter until 1996.

"These two events, the economy and our expansions, are combining to create more of a drag on third-quarter earnings than anticipated," said the company's statement.

Douglas Rockel, an analyst with Furman Selz in New York, said the series of announcements suggest that the third quarter will be very poor one for trucking.

"There's been additional price discounting in the regional market," said Mr. Rockel "I'm hearing weakness at other carriers, but not as bad as this. But hang on, there will probably be more announcements tomorrow."

American Freightways has seen double-digit revenue growth every year since its 1982 founding and saw 41.7 percent revenue growth last year.

"The third-quarter expansions are helping to re-establish momentum in revenue growth," the company said. "However, it is too early to predict that this will hold."