IF YOU like vegetables with all their nutrition, color and crunch intact and want to conserve cooking energy, the best cooking method is steaming.

Vitamin C and the B complex vitamins, found in green and yellow vegetables, are water soluble. When you blanch a bunch of broccoli in a large pot of boiling water virtually all the vitamin C (there is more vitamin C in a cup of broccoli than a cup of orange juice) dissolves out of the vegetable and into the cooking water. The more liquid used in the cooking process, the more C and B vitamins are wasted. The small amount of liquid that remains after steaming should be poured back over the vegetables or mixed with a little butter and/or lemon juice to make a light sauce.

Steaming vegetables will help keep their color, crunch and fiber structure intact. Beans, broccoli, Brussels sprouts, spinach and artichokes will be bright green. Asparagus, carrots, cauliflower, potatoes and corn will be firm and crisp. And because only a small amount of water is used, less energy is required.

An inexpensive and extremely versatile steaming device is the SteaMarvel. It consists of 18 perforated overlapping petals that unfold and expand. They rest on three short legs, holding ingredients above the steaming liquid. The SteaMarvel will turn any pot with a 6- to 9-inch diameter into a steamer. There is a post and a ring in the center of the unit for lifting the entire apparatus from the pot. In a small pot it's perfect for a few potatoes. In a large pot, it will handle a mountain of spinach. You can even stack corn on the cob in a criss-cross pattern and end up with a vegetable that is not water-logged. Every part of it is made of non-rusting stainless steel, and retails for about $5.

Shops that carry oriental cooking equipment offer a selection of tiered bamboo or aluminum steamers. Forever frugal with fuel, the Chinese devised multi-tiered steamers that will cook more than one dish at a time. The utensil consists of a series of 2-inch-high circular trays that sit on top of one another and are capped with a slightly domed lid. The bamboo models are available in diameters ranging from 4 to 16 inches and are used over a wok. Liquid is placed in the bottom of the wok to reach about an inch below the steamer. Ingredients are placed inside the tiers and cooked.

A modern version of the bamboo unit is available in aluminum. It consists of two identical 4 1/2-inch deep, 12-inch wide steamer trays with perforated bottoms that are set, one above the other, atop a 12-inch diameter, 6-inch deep pot for the liquid. Each selection has a pair of handles so the whole steamer or just part of it may be lifted.

The classic bamboo model has two drawbacks. The wood will absorb tastes and odors and food particles will get lodged between the woven strips. The aluminum model has three advantages. There is less heat loss from layer to layer because the metal is nonporous and the sections fit tightly together. Less energy is used because aluminum is an excellent conductor of heat and this model is much easier to clean. The only serious problem is that aluminum interacts with high acid ingredients causing stains, pits and discolorations.The bamboo models (11-inch diameter) retail for about $15 and the aluminum for about $18.

The ultimate tiered steamer will be available shortly from the Good Cooking Equipment Division of General Housewares. Its basic design is that of the tiered aluminum steamer described above, but it is constructed of enameled steel which will not iteract with any foods. It is expected to retail for about $25.

Whatever steamer (or pot to hold a folding steamer) you choose, make sure it has a close-fitting lid. However, the lid must be loose enough to allow some steam to escape, otherwise a dangerous amount of pressure can build up. A good steaming pot is both wide and deep so the steam can circulate around the food. Always be careful using a steamer. Open the top from a safe distance and tilt it away from you as you do so.