Wal-Mart Stores has set the tone for what is expected to be weak March sales reports from the nation's biggest retail chains.

The world's biggest retailer says sales excluding gasoline at U.S. stores open at least a year rose 0.7 percent in March, less than analysts' forecasts. Wal-Mart blamed cold weather, which hurt apparel sales, and an early Easter.

But the company was more optimistic about April and raised its forecast for the first quarter.

"Because of the Easter calendar change and its potential positive impact on the April sales period, we expect comparable store sales without fuel for the April four-week period in the United States to be between one and three percent," said Tom Schoewe, executive vice president and chief financial officer. "This guidance is slightly higher than our comparable sales guidance of the previous two months, which has been flat to two percent."

Citing better management of its inventory, Schoewe said Wal-Mart was raising its forecast for first-quarter earnings from continuing operations to 74 cents to 76 cents per share, up from an earlier forecast of 70 cents to 74 cents per share.

As a Banc of America Securities analyst wrote this week, a "tough economy is Wal-Mart's sweet spot.''