The pressure on retailers is escalating as shoppers take their time completing their holiday shopping, according to two key measure of retail sales. That's making it more likely that stores will see a rare drop in holiday sales from a year ago.

According to the International Council of Shopping Centers-Goldman Sachs index, same-store sales rose a modest 0.6 percent for the week ended Saturday from the previous week and slipped 0.4 percent compared with the year-ago period.

Same-store sales are sales at stores opened at least a year and are considered a key indicator of a retailer's health.

ShopperTrak RCT Corp., a Chicago-based research firm that measures traffic at more than 50,000 retail outlets, reported that total sales for the week ended Saturday edged down 0.3 percent compared with last year.

Shoppers have been increasingly delaying their holiday buying in recent years, but this year, as they grapple with job losses and tightening credit, the recession is playing a major role in consumers holding back.