For holiday entertaining it is every hostess' wish to have up her sleeve a dish for all occasions that is not only undeniably opulent, colorful and tasty, but also easy to prepare and serve.

Such a dish is Seafood Guacamole, a rich and stunningly spicy mixture of lump crab meat, avocado and fresh salsa, perfumed with cilantro. It can be served in that seldom-used fondue pot or chafing dish and can be put together ahead of time or at the last minute.

It is delicious served as an appetizer with fresh warmed nacho chips or toasted wedges of pita, or as a first course over a freshly baked biscuit or toast points. It is also an unusual pleasure served over a poached-egg-topped toasted english muffin for brunch. And, it is a natural as part of a buffet accompanied by crudite's or breadsticks. SEAFOOD GUACAMOLE (Makes about 6 cups)

6 tablespoons butter

2 shallots, minced

1 clove garlic, minced

1/4 cup medium sherry

1/2 cup red bell pepper, chopped

1/4 cup scallions, minced

1 pound lump or backfin crab meat, picked over

1/4 cup mayonnaise

1/2 cup plain yogurt

Juice and zest of 1 lemon

1 tablespoon cilantro leaves, minced

1 large, ripe avocado, 1/2 of it mashed and 1/2 of it diced

1/4 to 1/2 cup salsa*, to taste

Salt and freshly ground black pepper to taste

Hot pepper sauce to taste

Cilantro leaves for garnish

Heat butter in a large, heavy-bottomed saucepan and saute' shallots and garlic until limp. Add sherry and bring to a boil; cook over high heat for 1 minute. Stir in bell pepper and scallions and saute' over moderate heat until limp. Reduce heat to low and stir in crab, mayonnaise, yogurt, lemon, cilantro, avocado and enough salsa to give the right amount of spicy impact to suit your taste. If preparing ahead of time, refrigerate at this point in a tightly covered container.

To serve, reheat in a double boiler, stirring frequently, until very hot. Correct seasonings with salt, pepper, salsa, hot pepper sauce and/or lemon juice to taste. Garnish with cilantro leaves.

To serve as a dip, pour the heated mixture into an electric fondue pot (don't use the ones heated with Sterno; they don't heat evenly). Or use a chafing dish. Serve with warmed nacho chips, bread sticks, toasted pita wedges, crackers or crudite's.

As a brunch entree, for each serving, butter 2 toasted english muffins. Top each one with a poached egg and about 3 tablespoons of the mixture. Garnish with cilantro leaves. For a first course, spoon hot mixture over toast points or a freshly baked biscuit split in half. Garnish with cilantro leaves.

*Salsa, a tomato-based chili sauce, is available in jars in many gourmet stores and some health food shops.