American retailers including Macy’s are cutting prices by up to 75% on some items in a final pre-Christmas push after sales gains trailed last year’s increases.

Sales growth at stores open at least a year slowed to 3.5% in the week ended December 18 from 5.7% a year earlier, according to the International Council of Shopping Centers-UBS weekly index released today. Last week’s gain was the largest of the last four weeks, signaling a pickup in sales before the Saturday holiday.

“It reflects a last-minute and later push by consumers,” said the chief economist at New York-based ICSC, Michael Niemira. “Presumably this week will be a strong week. A third of our consumers we surveyed said they are shopping later than last year. It’s a trend.”

J.C. Penney stores were to open early at 7 a.m. today while Gap Inc. is advertising price cuts on sweaters and handbags as retailers try to boost sales after a lackluster start to the holiday season. Sales have been hurt because of sluggish job growth, Mr. Niemira said. American employers added 88,000 fewer jobs in November than the 200,000 forecast by economists.

Weather may play a role in getting shoppers to buy seasonal items including coats and hats this week as cold Artic air sweeps into the American Midwest and East, according to weather consulting firm Planalytics Inc. of Wayne, Pa.

The cold weather “should drive an uptick in seasonal demand during this critical shopping week,” a Merrill Lynch analyst, Daniel Barry, wrote. “A general trend of procrastination on the part of consumers so far this December should also contribute to an unusually sharp burst of shopping activity.”

Wal-Mart Stores, the world’s largest retailer, is forecasting December same store sales will slow to a 1% to 3% gain from a 4.3% increase last year. The retailer on December 18 said sales were rising within its forecast because of shoppers buying more food and general merchandise.

Lower-income shoppers that Wal-Mart and other discount retailers cater to have been hurt by rising energy prices as well as slower job growth. Gasoline prices last week were 22% higher than a year earlier.

Macy’s, a unit of Federated Department Stores Inc., is adding discounts for some items that total 75% off original prices and opening stores from 7 a.m. to midnight beginning tomorrow.

“The level of discounts has mounted significantly,” said Kurt Barnard of Retail Forecasting LLC in Upper Montclair, N.J.

Luxury chains such as Tiffany & Company and Neiman Marcus Group Inc.are expected to do better as higher income shoppers splurge. Neiman Marcus’s same-store sales rose 8.4% in November and compared with a 1.8% increase for 73 chains’ stores tracked by ICSC. Shares of the Dallas-based Neiman Marcus rose $1.47 to $72.50. Before yesterday, they had gained 32% this year.

ICSC forecasts same-store sales in the November-December holiday period will rise by 2.5% to 3%.That’s lower than the gain of as much as 4% he had projected at the start of the season for the sales, which exclude results from newly opened or closed locations.

“We may still get to an okay monthly number, but it all rides on how much of a lift there is this week and how much of a lift we get in the post-Christmas period,” Mr. Niemira said.

Only 31% of shoppers had finished their gift buying by Sunday night, he said.

“Our stores feel there’s going to be a lot of business yet this week,” said a spokeswoman for Bloomfield Hills, Mich.-based Taubman Centers Inc., owner of 31 American shopping centers, Karen MacDonald.

J.C. Penney and Sears, Roebuck & Company boosted traffic last weekend by being “super aggressive with early bird specials,” said the founder of America’s Research Group, Britt Beemer. “They had what consumers wanted. Consumers want 50% off.”

Gift-card sales and Internet sales are rising and may be cutting into purchases at traditional locations. Purchases of gift cards, which aren’t counted by retailers until recipients redeem them, may increase by $100 million to $17.3 billion this year, according to the National Retail Federation.

Internet sales are projected to rise as much as 26% to as much as $15.5 billion, according to ComScore Networks, an Internet research firm.

Retail Metrics LLC said profits at 138 retailers are forecast to rise by an average 9.1% during the fourth quarter, which for many merchants ends in January or February.

That compares with a 14.7% rise a year earlier, said Ken Perkins, president of Swampscott, Mass.-based Retail Metrics.