If the Grinch decides to come to Harvard Square this winter, he'll have one heck of a hard time trying to steal Christmas from local merchants.

Celebrating the first construction-free Christmas in seven years, Harvard Square businesses have exchanged detour lights for the twinkling kind and immersed the square in silver tinsel, colored garlands, and holiday cheer.

"Construction [of the new MBTA Harvard Square terminal] is complete and it is time to decorate," said Sally Alcorn, executive director of the Harvard Square Business Association. Businessmen said in the past the holiday spirit couldn't take root in a torn up square.

But the yuletide festive feeling has at last returned. At the Coop, there's as much Christmas decoration as merchandise. Included are 24 newly hand-painted banners representing Christmas themes, live fire-proofed poinsettia plants, wreaths, a huge outside Christmas tree, lights on the front of the store, and piped Christmas music outside the entrance to the store.

Grower's Market on Memorial Drive offers thousands of live Christmas trees, a Christmas shop with ornaments and artificial trees, and a menagerie of Christmas animals including a donkey, two deer, goats, two geese, and roosters.

Kupersmith Florist has set up an elaborate window display of bonsai plants and white lights which has "attracted a lot of attention," according to manager Al Brown. Emack & Bolio's has stocked up on holiday ice cream flavors including egg nog, rum, candy cane and the old traditional yuletide desert product cranberry ice cream.

The Harvard Square Business Association has hung more that eighty wreaths and red bows on Square lamp posts and hung over Mass Avenue two "light banners"--signs containg "750 twinkling lights in patterns resembling dancing stars and swirls," Alcorn said.

Not to be outdone by its older neighbor, Charles Square has joined in the spirit of Christmas decorating by setting up a 28-foot Christmas tree with 3000 multicolored lights and 2000 silver ornaments. In addition, the Square features a Santa Claus, carolers, wreaths, an art exhibition, and an old-fashioned cart with chestnuts, mulled cider, and dessert items called "Charles Squares."

Despite all these festive arrangements, sales are starting slowly for local businessmen, who generally look forward to the period between Thanksgiving and Christmas to generate the biggest sales of the year.

"Since Thanksgiving traditionally marks the beginning of the Christmas shopping season, and it occurred a week later than a year ago, the Christmas buying season began a week later this year," said James A. Argeros, president of the Coop.

"I'm hopeful that people will wake up to realize it's 16 days to Christmas and buying will be more intense," Argeros said.

One store is trying a unique Christmas time sales technique. "We're celebrating Christmas by being nice," said Larry A. King, manager at Au Bon Pain. "After January 1, we'll go back to being mean."