COOKING AN egg is not always the simple process it's cracked up to be. An egg shell, while nature's most perfect container in many respects, is easily shattered by sudden contact with boiling water. You end up with half a cooked egg and a sauce-pan filled with egg white streamers.

Some cooks protect eggs by placing them in a pan of cold water, bringing it to boil, turning off the heat and allowing the eggs to sit in the hot water until cooked to the desired hardness.I have gotten into the habit of bringing the water to a gentle simmer and lowering the eggs into the water with a Chinese strainer.

Whatever system you choose, it is important to make a small hole in the large end of the egg before cooking it. The inside of the egg expands rapidly when it comes into contact with hot water. It is that expansion and resultant pressure against the shell that most often causes cracking. The large end of the egg contains a small air sack. The tiny hole allows the air to be pressed out as the white expands. A membrane between the air sack and the white prevents additional seepage.

There are a number of devices available that will produce a perfectly sized hole in the egg. The best is made by Zyliss of Switzerland and distributed by Hoan. A small rectangular box measuring 3 inches-by-2-inches-by-1 inch contains a snap spring device with a small very sharp pin at the tip. A tab at the side of the box is pressed to release the pin. An oval indention on the top of the box holds the egg in proper position.

You may feel this tool is not absolutely necessary and the entire operation could be performed with a steady hand and a short pin. Well, you're right. Make sure the point is no longer than 1/4 of an inch and use a smooth, gentle motion. It's not difficult. The problem is keeping the push pin in the kitchen. They have a way of disappearing, while the Zyliss boxes tend to stay put. At $3.50 each, it is not a question of putting all your egg money in a single basket.

Two other egg "gadgets" not as easily replaced are sectioners and slicers.

The ideal tool for slicing an egg is an egg sectioner. The thickness and length of almost every knife is too great for this delicate job. Place the peeled egg into the petal shaped cup on the base. Push the metal ring down and the thin stainless-steel intersecting wires will slice the egg into six perfect sections. The cutting ring is returned to the starting position by a spring. The body is made of cast aluminum and is 5 inches high with a 3-inch-wide base. The Rowoco sectioner retails for about $6.50.

The most common egg slicer available consists of a plastic and chrome-plated frame with a series of stainless steel wires. The base has a double oval depression which allows slicing eggs either lengthwise or crosswise. It measures 4 inches by 3 1/4 inches and retails for about $3.

Believe it or not, there is an egg slicer constructed to professional standards. Made of heavy cast aluminum, it is molded into a ridged cup and a press frame inset with stainless steel cutting wires. Troughs inside the handles are fitted with a flexible piece of metal which provides the spring action needed for easy and complete slicing. A locking mechanism at the base of the handles keeps the utensil shut when not in use. The shape of the base cup and cutting frame permits both lengthwise and crosswise egg slicing. The slicer measures 7 1/2 inches-by-3 1/3 inches and retails for $7.50.

When using any egg slicing equipment, it is a good idea to wait until hard boiled eggs have cooled to room temperature. This allows the white and the yolk to develop a texture that will hold together during slicing. It also means a much smoother edge. Rubbing a little vegetable oil along the cutting wires will also assist in giving a clean slice.