NEW YORK » Americans spent briskly in October before Superstorm Sandy hit the Northeast, but they may not continue to do so during the busy holiday shopping season.

The International Council of Shopping Centers said today that its tally of 21 stores shows a 5 percent gain in sales at stores open at least a year in October, better than the 3.5 percent to 4.5 percent estimate.

But analysts worry that sales going forward will take a hit because many Americans bought generators and other storm supplies, which could cut into their budget for the holiday period. That would be bad for retailers, which can make up to 40 percent of their annual sales then.

The results cover the four-week period ending Oct. 27. November’s results will show the storm’s full impact.