Wilfredo Lee / AP Sales clerk Luis Sanchez rings up purchases Thursday at a Costco warehouse store in North Miami Beach, Fla.

NEW YORK — Caught in the maelstrom of higher gas and food prices, Americans — even more affluent ones — are seeking shelter in wholesale clubs and discount apparel chains.

Low-price operators Costco Wholesale Corp., Wal-Mart Stores Inc. and TJX Cos. reported better-than-expected sales on Thursday, while traditional apparel chains J.C. Penney Co. and Limited Brands Inc. struggled.

"The smart shopper is in full bloom," said Craig R. Johnson, president of consultancy Customer Growth Partners. "They're looking to stretch their household budgets, and if you can get decent quality merchandise, why pay full price?"

"Smart shopping" is sweeping through all wage classes, analysts say, and it could spell trouble for retailers' profits and for the economy.

To lure customers, apparel chains are discounting more. First-quarter profits are slated to be down by 14.9 percent, according to Ken Perkins, president of RetailMetrics LLC, a research company in Swampscott, Mass. That compares to a projection in January of 5.3 percent profit growth.

Retailers' first quarter ended in April and companies will start reporting their financial results next week.

Perkins and other analysts expect only a modest rise in sales in May and June as consumers spend tax rebate checks that are starting to arrive.

"There's too much going on," in the economy, Perkins said. He and others expect shoppers to use the extra cash to pay down debt and catch up on utility and food bills.

That could be a disappointment for the Bush administration, which had hoped the checks would give the economy a much-needed lift.

Because of an extra shopping day last month compared to a year ago, the retail industry expected sales to rise in April.

The UBS-International Council of Shopping Centers retail sales tally for the month rose 3.6 percent. That surpassed the 2 percent estimate and marks the biggest gain since March 2007, when the index was up 5.9 percent. The April performance followed a 0.5 percent decline the previous month, the weakest March in 13 years.

Sales for the two months combined were up a tepid 1.6 percent, in line with the average sales growth since the beginning of the industry's fiscal year. The surprise, however, was the growing gap between discounters and traditional retailers.

Discount chains registered a 3 percent same-store sales gain, while wholesale clubs posted a 9.2 percent gain. Meanwhile, same-store sales at apparel chain stores fell 1.4 percent, according to the ICSC tally.

Except for Wal-Mart, whose shares rose 33 cents to $57.16, investors pushed many retailers' shares down Thursday. Penney's stock fell 2.41 percent and Costco's lost more than 1 percent.

Eduardo Castro-Wright, Wal-Mart Stores U.S. president and chief executive officer, said in a statement that the "economy continues to get tougher" and customers increasingly are unable to stretch their dollars to the next payday. But that's also been a boon for the discounter, which has spruced up its stores and merchandise. It reported a 3.2 percent gain in same-store sales. Analysts polled by Thomson Financial expected a 2.1 percent gain. Including fuel, same-store sales climbed 3.8 percent.

Its business was fueled by strong sales in grocery and health items, and by entertainment products.

At an industry conference last week, the world's largest retailer said that more affluent customers are shopping at its stores now. For Wal-Mart's purposes, it considers shoppers with a household income of more than $55,000 to $70,000 affluent.

Target Corp. posted a 3.1 percent gain in same-store sales, below the 4.5 percent estimate, as consumers shopped for necessities such as food and skipped higher-priced items.

Costco's 8 percent increase surpassed the 6.1 percent estimate, helped by higher gas prices. Excluding fuel, same-store sales rose a solid 5 percent as shoppers were attracted to buying merchandise in bulk.

TJX, which operates discount apparel and home stores including T.J. Maxx and Marshalls, said same-store sales rose a better-than-expected 8 percent. Discount apparel chain Ross Stores Inc.'s 8 percent increase beat estimates, too.

Many mall-based apparel chains struggled.

Among department stores, Penney reported a 1.7 percent decline in same-store sales, better than the 4.6 percent decline analysts expected. Nordstrom Inc. posted a 3.8 percent drop in same-store sales, more than double the decline that Wall Street expected.

Limited reported a 5 percent drop in same-store sales, almost more than double the expected drop. Gap Inc. reported a 6 percent drop in same-store sales, more than three times what was projected.