Wal-Mart Stores, the nation's largest retailer and a bellwether for the economy, said Tuesday that its sales and profit surged in the first quarter as belt-tightening consumers flocked to its bargain prices.

But the giant discount chain also cautioned that it was not immune to the economic slowdown. The company said its earnings might come in at the low end of analysts' expectations for the current quarter because of higher transportation costs and customers facing problems between paychecks. It also predicted little, if any, growth in individual store sales.

"Our business is even more relevant to our customers today, given the current economic pressures," said H. Lee Scott Jr., chief executive of Wal-Mart. During the first quarter that ended April 30, Wal-Mart's profit increased 6.9 percent to $3.02 billion, or 76 cents a share, from $2.83 billion, or 68 cents, a year ago.