South Padre Island is at the tip of Texas, the southernmost in a thin line of fragile barrier islands that follow the coast from Galveston south along the curve of the Gulf of Mexico. It is so remote that the last land battle of the Civil War was fought in the cactus-dotted sandhills near there more than a month after the war was over. They hadn't gotten the word.

It's a resort area that mixes gulfstream charter-boat fishing, scuba diving among the offshore oil rigs, bird watching in the salt marshes, and border crossing trips into nearby Matamoras, Mexico, to eat real fajitas or bargain in the Mexican market for a stuffed armadillo.

In Port Isabel, on the mainland side of the causeway that leads to the island, is the La Posada art gallery in the renovated historic Queen Isabel Inn, which at the turn of the century served the since-abandoned railroad. The inn still serves as a small hotel, but the old dark paneled lobby walls are filled with multimedia art.

Gallery owner Mary Lou Campbell has turned the old hotel into a cultural center for the area. An environmental activist, Campbell frequently has the coffee pot going, orange juice in a glass pitcher and banana bread for the customers.

It also feeds committees whose members pull up chairs around the round oak table in the center of the room to develop strategies to watchdog the commercial developers on the fragile strip of barrier islands.

Hostessing a recent party, Campbell worked with Linnette Keller, a charterboat captain's wife who caters island parties with expert Tex-Mex party food.

Real Texans, they say, don't eat tamales with raisins, but Keller provided both versions in a menu of stand-up party food. The raisins sweeten the cornhusk-wrapped Mexican specialty. Visiting gringos tried both, but the Texans skipped the raisin version.

While staying at South Padre Island, we went to Mexico to have fajitas, which are the rage on both sides of the border now. Every barbecue cook has a personal version of the skirt-steak specialty, made from a sinewy cut of beef once sold cheaply. It's just two flat strips of beef from the lower ribs, tenderized by marinating, cut into narrow strips, grilled over charcoal very quickly, and served in a hot soft flour tortilla.

We drove to nearby Brownsville, parked on the Texas side of the border, and walked over the international bridge to Matamoras. Driving back and forth can get you stuck in border traffic jams and then confused in a tangle of little Mexican streets.

Once in Mexico, you can taxi to the restaurant of your choice, ours being Los Portales. Fajitas were listed at 1570 pesos, the highest price on the menu. Using a calculator to figure the peso/dollar difference that came to $6.37 as the price of the entree.

The fajitas and barbecued cabrito were served from a table-side grill where you could spear a slice of meat and fill a tortilla with meat, adding guacamole and salsa or sour cream.

In Port Isabel, lunch at a working man's cafe turned up some unfamiliar specialties in the menu posted on the wall.

Locals were having rib-sticking platter-sized flour tortillas folded around an omelet of either eggs and potatoes or eggs and chorizos. Another filling was a meat stew in 12-inch diameter soft tortillas.

Delicious as all the Tex-Mex food was, one of our favorite pauses on South Padre Island was for what they call border buttermilk. A trip to that area is an enjoyable experience, but it is also true that a blast furnace heat pummels south Texas in the summer. For that reason, the simple but cooling border buttermilk is so welcome. FAKE FAJITAS (Serves 6)

The barrier to making real fajitas is the scarcity of skirt steaks. Some markets carry them occasionally. This recipe using flank steak is a good substitute. (If you should find skirt steaks, they should be flattened, cut sharply across the grain into thin strips (about two inches wide), marinated as directed below and briefly charcoal grilled.

1 flank steak, about 1 1/2 pounds

12 flour tortillas, 10-inch if available

Salsa, guacamole, avocado slices and sour cream for serving

FOR THE MARINADE:

1/4 cup olive oil

1/4 cup white wine vinegar

3 cloves garlic, minced or pressed

1/2 teaspoon salt

1/2 teaspoon oregano

1/8 teaspoon pepper

Mix together marinade ingredients in shallow glass dish large enough to hold steak. Marinate steak, covered and refrigerated, for at least 6 hours or overnight. Turn occasionally.

Before serving, cook steak until rare on charcoal grill. Allow 5 to 8 minutes for each side. Remove from grill to cutting board and slice across the grain into very thin slices.

Heat tortillas by placing them, one at a time, directly on the charcoal grill, for a total of 30 seconds, turning once, until hot and soft. Do not overcook or they will dry and harden. Keep warm by wrapping in hot damp cloth or in foil in a 275-degree oven.

Serve the sliced meat on the warm tortillas with salsa, guacamole, avocado slices and sour cream. Roll up and eat either with fingers or fork. TOMATO SALSA (Makes 1 1/2 cups)

2 medium tomatoes, peeled, seeded, chopped finely

1 tablespoon olive oil

3 scallions, minced

2 tablespoons canned chopped green chilies

2 tablespoons fresh coriander, chopped

1/2 teaspoon salt

1 avocado, peeled, seeded, chopped (to be added or served separately)

In a nonmetallic bowl, mix together all ingredients except avocado. Cover and refrigerate.

When ready to serve, add avocado (or serve separately.) LINNETTE KELLER'S CHINGALINGAS (Makes 36 appetizers)

South Padre caterer Linnette Keller likes to vary the "heat" of her Mexican cocktail party food. This crispy fried tortilla concoction has no chili in it, but it is served with a salsa dip to give it a kick.

3-pound chicken

1 teaspoon salt

2 cloves garlic

1 bay leaf

1 tablespoon vegetable shortening

1 small onion, minced

1 green bell pepper, seeded and diced

2 large tomatoes, peeled, chopped

1 teaspoon chicken bouillon granules

12 8-inch flour tortillas

Oil for frying

Salsa and sour cream for serving

In a large kettle, place chicken, salt, 1 clove garlic and bay leaf in enough water to cover. Simmer 1 hour, or until very tender. Remove chicken from broth and let stand until just cool enough to handle. With fingers, shred chicken, reserving pieces of skin. Finely chop skin and set aside.

In a large skillet, melt shortening and saute' onion and bell pepper until soft, about 5 minutes. Add second clove of garlic and saute' another minute. Add shredded chicken, tomato and chicken bouillon granules. Reduce heat, simmer, stirring until nearly all liquid is absorbed.

In another skillet fry pieces of chicken skin until brown and crisp, about 10 minutes. Add to chicken mixture and cook another 5 minutes. Mixture will be nearly dry.

Steam tortillas soft* (or soften 10 seconds in microwave oven). Place about 1/4 cup chicken filling at bottom edge of tortilla. Roll up, tucking in ends. Secure flap with toothpick. Repeat with remaining tortillas. Cover with damp cloth to keep from drying out.

Heat oil in deep fryer to 350 degrees. (If oil is not hot enough, tortillas will be tough.) Add chingalingas in batches and fry until golden brown, about 3 minutes per side. (Or fry in 1 inch of hot oil in a skillet, turning once, until golden brown.) Drain on paper towel. Remove toothpicks.

Serve whole or slice each roll into 3 or 4 pieces. Serve with bowls of salsa and sour cream.

* To soften tortillas: Remove from refrigerator about 30 minutes before needed. Dip hand in water and brush over each side of tortilla. Place on a rack over boiling water. Heat one at a time. If properly dampened, they won't crack when folded and will be flakier and more tender when fried. TORTILLA DE HUEVOS IN BIG FLOUR TORTILLA (4 servings)

Tortilla is a word that refers not only to the familiar flat, round bread, but it also can identify a Mexican or Spanish omelette. At South Padre, the combination of the two "tortillas" produced the filling lunch special, but it could also make an interesting Mexican brunch item.

The 12-inch tortillas are not usually found in the stores here. But sometimes the 10-inch ones are available in specialty markets.

Optional variations to this omelette are the addition of cooked and crumbled chorizo sausage, chopped green olives or saute'ed chopped onion.

4 big flour tortillas, at least 10-inch size

8 eggs, slightly beaten

2 to 4 tablespoons chopped, canned green chilies

4 small red bliss potatoes, cooked, peeled and diced

Salt to taste

2 tablespoons butter

Soften tortillas by quickly heating or frying on a griddle until they are just soft but not crisp. Keep warm in foil or covered dish in warm oven.

In a bowl, combine eggs, chilies, potatoes and salt. In a frying pan, melt butter over medium-high heat. When butter just begins to brown, add egg mixture. When bottom begins to set, lift edges to let uncooked portion flow underneath. When top is nearly set remove from heat.

Cut into 4 servings. Place a tortilla on a plate, on this place a serving of omelette and fold the tortilla in half. BORDER BUTTERMILK (Makes 6 drinks)

Milk is not one of the ingredients. Pink lemonade makes a prettier drink but it is not authentic border buttermilk. It can also cool off the non-drinkers or the kids by simply leaving out the rum.

6-ounce can frozen lemonade

6 ounces white rum

Crushed ice to fill blender

Place all in blender and blend at low speed until thick and frothy.