“We’re going through a tough time here,” Mr. Mackey said in a conference call with Wall Street analysts. “I’ve never seen our comps this low in the 30 years I’ve been with the company.”

Image The fish counter at the Whole Foods store in Edgewater, N.J. Whole Foods is slowing its expansion plans as growth falters. Credit... Suzanne DeChillo/The New York Times

Shares of Whole Foods, which had already dropped 44 percent since the first of the year, dropped nearly 18 percent in after-hours trading, to $18.84.

Because of the slowing sales, Mr. Mackey announced that the company would reduce the number of stores it plans to open in fiscal 2009 to 15, instead of 25 or 30. He also said the company would aggressively cut administrative costs and discretionary capital expenses not related to store openings.

The company’s weak report comes amid a difficult time in the supermarket industry, one in which consumers are trading down to cheaper products and discount stores.

Whole Foods is trying to recast its upscale image by offering more store label products, which are cheaper, and more sales, not only among grocery items in the center of the store but also in the produce, seafood, meat and prepared foods sections on the perimeter of the store where the company makes most of its money.