Although shoppers have been hitting the stores this Thanksgiving weekend with a holiday fervor, Harvard Square retailers said they are having a hard time being optimistic about how they will fare during this Christmas season.

Traditionally, consumer spending the day after Thanksgiving has been a good indicator of how successful the holiday season will be for retailers, said Jerry Berkeley, assistant manager of Discount Records on JFK St.

But if this past weekend is any sign of how much money consumers will unload on the city's shops in the upcoming weeks, employees at several stores in the Square said yesterday, there may not be much celebrating in these stores this month.

At J. August, a store that sells insignia items, sales have slowed considerably compared to last year, said John C. Ballestas, the store's assistant manager.

"We're really behind how we did last year," Ballestas said. "Maybe by as much as 15 to 20 percent."

Campus Exchange, another clothing store, located on JFK St., is apparently doing no better. A store employee, who requested anonymity, said the shop's profits are well below what they were last year at the same time.

"Last Sunday, we made half of what we did last year, and I think today we're at about a third of how we did last year," the worker said.

But other retailers said it is diffi- cult to compare this year's figures to those of 1990. At this date last year, stores had six extra post-Thanksgiving shopping days under their belts.

"We did as well this Friday after Thanksgiving as we did last year. But by not having six more days of shopping, it's too early to tell how we will do this season," said Allan E. Powell, general manager at the Harvard Coop.

Powell did say, however, that if current trends of consumer spending persist, sales at the Coop this month will fall short of last year's figures.

Not everyone in the Square is worried about the upcoming shopping season, however. Al C. Maroun, assistant manager at the Body Shop, an environmental products store on Mass. Ave., said his shop was doing well despite the state of the economy.

"We weren't here last year, but using last year's numbers from comparable stores, our head office projected a target for us, and we are above the target," Maroun said.

"We expect a really good season, and we don't expect this 'supposed' recession to keep us from doing well," Maroun said