A LONG WITH crocuses, jonquils and budding green beans, are the back yard grills. Nature need do nothing to enhance the excitement of spring. Outdoors cooks, however, could and would do much to bring variety and style into grill cooking if they developed acquaintance with marinades. The eternal and simple hamburger, hot dog and steak are all very well, but grills, like most things in life, profit from variations.

These delectable marinated dishes are in fact preparing themselves while you sleep, work or play. Just pour on the marinade, which takes but minutes to mix, and forget about it until time to put the meat on the grill.

Developed as a method for tenderizing less costly meats, marinades achieve even greater results when used on today's high-quality foods. Marinades not only enhance the quality of the meat, they also add subtle flavors and spice your garden or terrace with subtle and appetizing aromas.

After you have tried these marinades you will find that, with a little imagination, you can come up with a host of variations. One warning; Marinades involving sour cream or other dairy products are best avoided on very hot days.

Marinated meats because of their accentuated flavor are equally good, although quite different, served cold. You can have a delicious second meal without extra work by preparing for left-overs.

Just in time for the grills, New Zealand lamb has arrived on the market at a most advantageous price. A leg of this frozen lamb maybe a bit less tender and tasty than the domestic higher priced lamb but, happily, the marinades corrects these deficiences while adding much and saving more.

Shoulder of lamb is always less costly than leg and serves equally well for shish kebabs. The shoulder may also be substituted for the butterflied leg, but as it is difficult to remove the shoulder bone it should be grilled as is. It will take a bit longer to cook and, of course, will not be as easy to slice. MARINATED LAMB FOR THE GRILL (6 servings)

The flavor and aroma of this marinated lamb evokes the exotic Middle East where lamb is the principle meat and where it is treated with imagination. It is less work to prepare than shish kebab and I think you will find it more exciting. 3 to 4 pounds leg of lamb or shoulder, butterflied 2/3 cup olive oil 1/4 cup lemon juice 1 teaspoon salt 1/2 teaspoon pepper 2 tablespoons chopped parsley 2 teaspon oregano 3 bay leaves, crushed 1 cup finely sliced onions 3 cloves garlic, pressed or minced 2 teaspoons coarse salt

Have the butcher debone the leg or half leg of lamb and slash it so that it lies flat, like a butterfly with wings spread. Place it in a flat shallow pan or dish and cover with the remaining ingredients, except the coarse salt. Cover the dish, refrigerate and let the meat stand in the marinade for 12 to 24 hours. It is best grilled on an open fire, but is also exceptionally good if grilled under a broiler.

Put the meat side up on the grill or under the broiler. Spread the coarse salt on the surface, pressing it well into the meat. It will form a brown crust. Turn the meat after 5 to 10 minutes, depending on the thickness of the lamb and your preference for degree of doneness. Baste the meat with the marinade every few minutes while it is cooking.

When the meat is done put it on a wooden board and cut into slices about 2 inches thick. Serve with rice pilaf or potatoes au gratin. MARINATED FLANK STEAK (6 to 8 servings) 2 pounds flank steak in one piece 1/2 cup olive or vegetable oil 2 tablespoons vinegar 1 large clove garlic, crushed or minced 1 medium onion, sliced 1 bay leaf crumbled 1/4 teaspoon thyme 1/3 teaspoon rosemary 1/3 teaspoon pepper

Place the flank steak in a shallow dish large enough to allow the meat to be spread out. Pour on the oil and vinegar and distribute the garlic, sliced onions and herbs evenly over the entire surface. Place the dish in the refrigerator covered loosely for at least 12 hours and at most 2 days.

Grill the meat over hot coals, or under the broiler, 2 to 3 minutes on each side. As the flank steak is thin, be careful not to overcook it. Place the cooked steak on a wooden board and slice on the diagonal with a very sharp knife into very thin strips. Serve with potatoes, a green vegetable and salad. ARMENIAN SHISH KEBAB (6 servings) 3 pounds leg of lamb or shoulder, cut into 1-inch cubes 3 cloves of garlic, crushed or minced 1 1/2 teaspoons salt 1/2 teaspoon ground ginger 1/2 teaspoon allspice 1/2 teaspoon ground cloves 1/2 teaspoon paprika 1/2 teaspoon ground black pepper 1 pint sour cream

Mix all the spices together in a large bowl. Roll the cubes of meat in the spices until they are evenly coated. Pour on the sour cream, stir to distribute it among the cubes of meat. Cover and store in the refrigerator for 2 to 3 days.

When ready to grill thread the meat on skewers with alternate pieces of tomato, green pepper and, if you like, onions. Grill the shish kebab until brown on all sides but still slightly pink inside, about 10 minutes, turning every few minutes. Serve with rice pilaf, a green salad and crusty bread. ORIENTAL GRILLED CHICKEN (6 servings)

These succulent chicken morsels are also delicious cold so plan to have leftovers. 1 chicken (3 to 4 pounds) chopped into pieces about an inch square 1 tablespoon finely chopped fresh ginger or 2 teaspoons powdered ginger 2 cloves garlic, crushed or minced 1 medium onion, finely chopped 2 tablespoons sugar 2/3 cup soy sauce 2/3 cup dry sherry

Place chicken pieces in a large bowl. Combine all other ingredients and pour over the chicken, stirring to distribute it evenly. Let stand in the refrigerator overnight or at least 12 hours.

Thread the chicken on skewers with alternate cubes of pineapple and fresh green pepper. Place the skewers on the grill or under a broiler, turn the skewers from time to time so that the meat cooks on all sides, baste as you turn. It should take about 20 minutes in all.

Serve with rice, green salad and hot rolls. GRILLED GREEK CHICKEN (6 servings) 2 small frying chickens, cut into serving pieces 3 lemons, juice and rind 4 cloves garlic, crushed or minced 1 large onion, chopped 1 teaspoon each of oregano, thyme rosemary and marjoram 1 cup dry white wine Salt and pepper to taste

Squeeze the lemon juice into a large bowl. Add the cut up lemon rind, garlic, onion, herbs, wine salt and pepper. Put the chicken parts into the marinade, cover and place in the refrigerator for at least 24 hours. Turn the pieces of chicken at least 4 times during this period.

Grill over hot coals until very tender when piered with a fork, about 30 minutes. Baste with marinade every few minutes while grilling.

This chicken can also be baked. Arrange in a shallow pan in a single layer. Pour on the marinade and bake at 375 degrees for 1 hour, basting several times during this period.