The nation's retailers are winding down from what looks like their best holiday performance in a decade.

Early research has led some retail experts to believe that online purchases will soar past the astronomical increases already predicted. And traditional stores prospered as well, benefiting from a high turnout of shoppers whose spending was energized by a strong economy and a rising stock market. Even a snap of chilly weather in the year's final two weeks helped.

"If you didn't do well, you've got some problems, because this is a great year for retailers," said William Ford, senior economic adviser for TeleCheck Services Inc., which authorizes purchases by check.

TeleCheck reported a 6.2 percent gain in same-store sales--an industry barometer that measures revenue at stores open at least a year--between the day after Thanksgiving and Dec. 26 over the comparable period a year before. It was the biggest surge in sales recorded in at least 10 years, Ford said.

Sales were so swift that the National Retail Federation says its early projections may have been too conservative. The District-based organization had estimated that retail sales would rise as much as 6.5 percent, to $185 billion, in the last two months of the year. But it now says revenue could climb 7 percent, to about $199 billion.

"I think everyone expected to see sales moderate from 1998," said Pamela Rucker, a spokeswoman for the retail group. "They just assumed the economic juggernaut would slow down. But it didn't."

At Potomac Mills in Prince William County, some stores are now expecting revenue increases of up to 30 percent during the last two months of the year. The performance of jewelry, leather and children's stores was "absolutely phenomenal," mall manager Jim Ralston said.

Other top performers included consumer electronics, toy and home furnishings retailers, according to merchants and industry analysts.

At Circuit City stores, customers snapped up just about anything digital: cameras, digital video disc players and DVD movies. Prices have plunged on digital products over the past year, making them more affordable.

"We experienced an incredible amount of enthusiasm from customers for digital products," said Morgan Stewart, a spokesman for Circuit City Stores Inc. in Richmond.

Next month, Wal-Mart Stores Inc. said it will report that Wal-Marts met sales projections. Brisk business at Sam's Club stores during the week before Christmas will further boost the company's performance, a company spokesman said.

What's good news to retailers is bad news for bargain hunters, who will find slim pickings on the clearance racks later next month, retail experts say.

"If you want a good selection of winter clothes, you'd better go get it now rather than wait for the sale, when you'll find the wrong sizes and the wrong colors," said TeleCheck's Ford.

Not everyone kept up with the trend, however. Sears and J.C. Penney department stores have reported flat same-store sales in December compared with last year, partly because consumer buying habits have moved in new directions, leaving the two merchants scrambling to find a comfortable niche.

Retail spending over the Internet this season is expected to climb to $6 billion, double last year's total, according to Internet research firm Jupiter Communications. But some online merchants buckled under the stress of the holiday shopping season because they did not prepare properly or faced unexpectedly heavy Web traffic.

During peak shopping periods, e-commerce sites such as Toysrus.com and Kbkids.com had a difficult time keeping their online stores open. Last week, an overwhelmed Toys R Us told some customers it would not be able to ship their online orders in time for Christmas.

"The [online] sites that didn't have a strong holiday and aren't carrying momentum into 2000 are going to have a hard time capturing market share," said Mike May, an analyst with Jupiter Communications.

Healthy Holiday Spending

Holiday sales for retailers in the District and Maryland increased more than the national average, according to TeleCheck Services.

Percent change in same-store sales from previous year

Nov. 26 - Dec. 26, 1999

National 6.2%

Mid-Atlantic 6.4%

West 6.2%

Southwest 6.1%

Midwest 6.0%

D.C. 6.8%

Maryland 6.7%

Virginia 6.1%

SOURCE: TeleCheck Services

CAPTION: A New York Macy's shopper uses after-Christmas sales Sunday to get a jump on next year's holidays.