Retail sales slipped 0.1 percent in April, but sharp upward revisions to March's sales data indicated that the debilitated national economy is beginning to flex its muscles.

The Commerce Department originally said last month that March sales were down 0.8 percent, leading many observers to say that the economy was showing no signs of recovery.Revision of that figure upward nearly a full percentage point to a 0.4 percent gain makes the slight sales decrease in April less worrisome. A Commerce Department spokesman said the revision was "well within historical parameters."

"Despite the fact that sales went nowhere in April, the fact is that they went nowhere from a significantly higher level," said Robert Dederick, chief economist at Nor-thern Trust in Chicago.

April's decline in sales would have doubled to 0.2 percent without counting sales of cars, vans and trucks, which rose a surprising 0.3 percent. Much of that increase probably came in used cars, because the Big Three automakers all reported dismal sales in the month.

Sales of building materials, hardware, furniture and home furnishings all rose in the month. Analysts called that increase significant because it indicates that an improving housing market is drawing more customers into the stores to furnish their new homes.

The government said total sales of durable goods were up 0.6 percent in the month.