Even in midwinter it's easy being green. Just finish off the same old noodles or another supper of fish with a fresh, tangy herb sauce. It couldn't be more simple or readily available: Combine fresh parsley, watercress and scallions with olive oil and dijon-style mustard. And go from there.

Take the basic recipe and add fresh lemon juice and rosemary for broiling on fresh swordfish steaks. Toss the herb sauce with freshly cooked carrots, green beans or zucchini. Serve the sauce with fresh tomato pasta for a light first course. To dress fettucine salad, add garlic and basil to the basic recipe. Lastly, combine the sauce with three cheeses to stuff cannelloni or jumbo pasta shells.

To make the sauce, look for full bunches of parsley that are firm, not droopy. The leaves should be bright green. To clean parsley, place a large pot in the sink and fill with cold water. Remove elastic from base of parsley. Hold parsley upside down and grasp stems firmly. Dip parsley up and down several times in water to remove sand. Repeat with clean water if necessary. Shake parsley against sink to remove excess moisture. Pull only leaves from the bunch and place in a clean tea towel. Roll up to dry. One large bunch of parsley will yield about 3 cups of loose leaves or 3/4 cup minced leaves.

The watercress should be perky with dark green leaves. Discard any bunches that have yellow leaves. They will be too old. To clean watercress, remove elastic band and pluck the leaves off with no more than one half inch of stem left on. The stems are too bitter. Place leaves in a strainer and rinse several times with cold water. Place in a tea towel to dry.

Choose scallions that are small. Use the white part of the onion and no more than two inches of the green stem. Dijon-style mustard and olive oil are available in the speciality food sections of grocery stores.

With minor changes the sauce can complement a variety of dishes; for salmon steaks, as an example, use tarragon in place of the chervil. To add dried herbs, place the leaves in the palm of your hand, and rub with the heel of the other hand. The heat and friction of the rubbing will release flavor from the oils in the leaves. HERB SAUCE (Makes about 1 1/2 cups) 1 large bunch parsley 1 bunch watercress 1 bunch small scallions 1 tablespoon dijon-style mustard 1/2 to 1 teaspoon salt Freshly ground black pepper 3/4 cup olive oil

Wash and clean parsley, watercress and scallions. Discard stems of parsley and watercress. Mince parsley in the work bowl of the food processor with the steel blade. Add watercress and mince. Add scallions, cut into 1-inch pieces and mince. Add dijon-style mustard, salt and lot of freshly ground black pepper. With the machine running, slowly add the olive oil. The sauce will be thick. Add up to 2 more tablespoons olive oil if desired. Taste for seasonings.

To store, place in a non-metallic container. Cover the top of the sauce with plastic wrap to prevent discoloration. Cover with a lid. The sauce will keep refrigerated up to 3 weeks, or freezes well. SWORDFISH STEAKS (4 servings) 1/2 teaspoon corn oil 1/4 teaspoon dried rosemary or 1 teaspoon dried chervil 3 tablespoons fresh lemon juice or lime juice 1/2 cup, plus 2 tablespoons herb sauce (recipe above) 1 1/2 pounds swordfish steaks, 3/4-inch thick

Preheat broiler and broiler pan for 5 minutes. Lightly oil pan just before placing steaks on it. Stir rosemary or chervil, lemon juice and herb sauce together. Divide evenly between tops of steaks. Broil 4 inches from heat for 6 to 8 minutes until opaque and springy to touch. Do not overcook!

Serve with boiled red potatoes and steamed broccoli. Pass additional lemon wedges. FETTUCINE SALAD WITH ROASTED PEPPERS (8 servings) 1 1/2 cups basic herb sauce (recipe above) 2 tablespoons dried basil 3 large cloves garlic, minced 3/4 pound dried fettucine noodles, plain or spinach 4 ounces roasted red peppers, canned or in jar, drained 1/2 cup toasted slivered almonds

Mix herb sauce with basil and garlic. Set aside. Bring a large pot of salted water to a boil. Add pasta and cook, stirring often, for 8 to 9 minutes until al dente. Drain, and cool with cold running water. Drain well. Toss fettucine with 1/4 cup dressing to prevent sticking and to keep pasta moist. This may be done the morning of a party. Refrigerate covered.

Remove from refrigerator several hours prior to serving. Cut peppers into 1/2-inch squares. Add 3/4 cup dressing by large spoonfuls and toss fettucine until well coated with sauce. Add more dressing if needed. There should be no dressing, however, in the bottom of the serving bowl. Add peppers and almonds and toss gently. Taste for seasonings. Serve at room temperature with cold sliced meats, and green bean and baby corn salad. TOMATO PASTA (8 first-course servings) 4 large eggs 4 tablespoons tomato paste 2 tablespoons olive oil 1 teaspoon salt 3 1/2 cups flour Extra flour for kneading

In a small bowl, beat eggs with a fork. In a larger bowl, mix tomato paste with oil to form a smooth paste. Add salt. Gradually add eggs and mix until smooth. Place flour on counter and make a large well in the center. Put the egg mixture in the center. Beginning at the inside edge of the flour, work a small amount of flour into the egg. Use a circular motion. Keep the tines of the fork flat against the counter top.

Work slowly around the inside of the circle until half the flour is incorporated. Toss in remaining flour with fork. Knead mixture for several minutes until flour is incorported, and dough is smooth. Do not mix in any hard bits of flour.

Set pasta machine at widest setting. Divide dough in quarters. Run one piece through the machine once. Flour dough lightly on one side. Turn over. Fold dough in 3 to form a rectangle about 4-by-3 inches. Tap with knuckles along length of dough. Place open end in machine and run through on widest setting. Repeat 6 to 8 times until dough becomes springy and somewhat dry. Set machine one notch lower. Run unfolded dough through each lower setting. For linguine, dough should be 1/8-inch thick, fettucine 1/16-inch thick. Drape dough and allow to dry 15 to 30 minutes until machine will cut dough without the strands sticking together. Run dough through appropriate setting to cut. Cover trays with clean tea towels. Spread pasta on towels. If storing for several days, toss with lots of semolina to keep strands separate, then dry slightly and store in plastic bags, refrigerated. If using immediately, use a bit of semolina and cook in batches. Repeat procedure with remaining dough.

To cook pasta, bring lots of heavily salted water to a boil. Shake excess semolina from pasta. Cook pasta in two batches. Add pasta to water, bring back to a boil, and cook 1 to 2 minutes. Drain in a colander. Do not rinse. Toss gently with spoonfuls of the herb sauce until well coated. Serve warm. CANNELLONI WITH SHRIMP AND ARTICHOKE SAUCE (Makes 8 cannelloni) Pasta: 2 large eggs 1 teaspoon salt 1 tablespoon olive oil 1 1/2 cups flour Sauce: 2 tablespoons olive oil 2 large garlic cloves, finely minced 3 scallions, finely chopped 1 teaspoon basil 28-ounce can italian plum tomatoes, drained 1 1/2 tablespoons tomato paste Salt, pepper 8 shrimp, peeled 8 artichoke hearts, halved Filling: 3/4 cup dry ricotta cheese 1/2 cup mozzarella, shredded 2 ounces fresh grated parmesan cheese 1 egg 1/4 cup basic herb sauce (recipe above) Salt, white pepper Nutmeg Dash hot pepper sauce 1 medium zucchini, julienned

For the pasta, place the eggs, salt and olive oil in the work bowl of the food processor fitted with the steel blade. Process 10 seconds. Add the flour all at once and process with on/off turns until a ball of dough forms, about 30 seconds. Remove ball from food processor and knead for several minutes on a lightly floured counter. If dough is too moist, add more flour until your hand does not stick to the dough.

Set the pasta machine at widest setting. Divide dough in half. Run one piece through the machine once to flatten. Flour dough lightly on one side. Turn over. Fold dough in 3 to form a rectangle about 4-by-3 inches. Tap with knuckles along length of dough. Place short end in machine and run through on widest setting. Repeat 3 to 4 times. Processor dough requires fewer times than dough made by the traditional method. Set machine one notch lower. Without folding dough again run through each lower setting down to second setting from the end. If dough is too thin, it will tear with filling. Repeat kneading with second piece of dough.

Cut pasta into 8 5-inch squares. It is not necessary to let pasta dry. Drop into a large pot of boiling water, stirring constantly. Cook for 1 to 2 minutes. Drain, rinse with cold water and set aside until ready to fill.

For the sauce, saute' scallion and garlic in olive oil on low heat for 3 minutes. Add basil. Process the drained tomatoes and tomato paste until smooth in the food processor, or mash with the back of a large slotted spoon to break up tomatoes. Add to scallion and garlic and simmer 15 to 20 minutes until thickened. Season with salt and pepper. Set aside.

For the filling, mix the ricotta, mozzarella and parmesan cheese in a large bowl. Whisk the egg separately and add to cheese. Stir in herb sauce and seasonings. Fold in zucchini, and chill filling before using if necessary to firm it up.

To assemble the dish, place a heaping spooonful of filling near one end of a cannelloni square. Roll and place in a buttered 8 1/2-by-11 inch dish. Repeat with remaining filling and squares. Do not overlap filled squares.

Arrange artichoke halves around canneloni, and pour tomato sauce over canneloni and artichokes. Bake uncovered at 375 degrees for 15 minutes. Halve shrimp lengthwise, and place in dish 6 minutes before end of cooking time. Serve with romaine and cucumber salad and fresh italian bread