Thanksgiving week is a good time to give thanks for the memory of some special event -- and perhaps to wonder what made it special.

One man who I know would choose the time he walked into a party and a pretty blond stranger flung herself into his arms. A fantasy fulfilled, and an evening that was an instant success.

The unexpected also figured in the party Lucy Moorhead, author of "Entertaining in Washington" (G.P. Putnam) and his wife of Rep. William S. Moorhead (D-Pa.), chose as most memorable this year.

"It was a birthday party -- only 16 or 17 people, mostly family -- and the thing that made it special was a surprise piano player. He came bringing his own electric piano -- with speakers too, so you got a phenomenal amount of sound. Up went a couple of rugs in the hall and we all had a wonderful time. We started with a foxtrot and wound up with a version of the Virginia Reel. A lot of people don't realize that you don't have to have a piano to hire a piano player."

Two people Mrs. Moorhead knows who will bring an electric piano and play for you and Frank Coviello (234-0806) and Bob Vigoda (893-4544).You probably could hire a blond, too, but that seems like cheating.

Duke Zeibert's favorite party took place about a month ago at his restaurant. It was a surprise party to celebrate political consultant Mark Shields' move to The Washington Post.

"The food was outstanding and the big hit was the raw bar and steak tartare.

Everyone came -- media, politicians. Sensational food and people who just blended and mixed. What else makes a party?"

Catherine Macripodari, owner of the Gourmetisserie caterian service, 1624 Wisconsin Ave. NW, would add beauty. On a recent rainy Sunday, she catered a party given by the National Council of Negro Women to celebrate the opening of the Mary McLeod Bethune Museum.Guests walked out of the gloom and into a candlelit room where round tables were draped in soft green cloths, topped with overskirts of rust velvet. "I used a great deal of my copper collection -- a copper tray on the table, the candles were in brass candlesticks and all the glasses were crystal."

The party was a huge success -- possibly in part because of Mrs. Macripodari's attention to detail.

In addition to making a space beautiful, she feels you have to make it fit the party. Stuck with a cavernous room? She would block part of it off with plants. Too little space? Stagger the hours you invite guests. She also tries to provide food that people aren't going to run into everywhere -- spanakopitta , for instance, or rumaki .

"In a city like Washington, people quickly tire of the monotony of the catered party. You have to provide fresh menus and fresh ideas."