BY ELIZABETH VALENTIK Irish-Mexican pairing works      There is a new spot in Brunswick that should not be missed if you enjoy plenty of good food in a friendly atmosphere.      Pedro O'Hara's serves two styles of ethnic foods, as the name implies, and it does it with flair and a sense of humor. Pedro's is downstairs in a historic building on Brunswick's main drag, the former digs of a nightclub. Tables fill the raised dance floor/band stand, with a shiny brass railing surround. The ceiling is covered with mirrors that reflect the strings of red and green hot-pepper-shaped lights draped around the edges of the room. The bar, separated from the dining area by a half-wall, seems to be pretty much the Irish half of this theme-team, with its neon shamrocks, decorative beer-tap pulls and mirror back of the bar.      Half of the menu is Southwestern-Mexican, the other half is Irish pub fare, and there is even a bit of stir-fry tossed in for good measure. As we looked over the very substantial menu, our crackerjack server brought us warm corn chips with "Pedro's Picante" salsa. (In other quarters it might be called Pico de Gallo). This is a very tasty creation, in-house-made of very fresh ingredients, and nicely spicy, not hot. It's a pleasant offering to the customer who must take some time to choose from the listings of many Irish and Mexican dishes.      Some of the menu choices for appetizers are: Pedro's fries, $1,95 and $3.95; Snake Bites, which are stuffed Jalapeno peppers, $5.95; quesadillas, $4.95, with beef, chicken or mushroom, $5.95; nachos, $5.50, with beef or chicken, $6.50.      Main-course offerings include: tequila lime chicken, $9.95; lazy fajita wrap, $8.95; burritos or enchiladas, $7.95 each; tacos, $6.95; charbroiled steak tips, $9.95; charbroiled lamb tips, $10.95; chicken stir fry, $9.95; veggie stir fry, $7.95. The burgers are a half-pound of ground beef on a bulkie roll with lettuce, tomato and pickle, with fries, costing from $5.50 to $6.95, depending on the topping combos chosen. The Penhallow is a char-grilled chicken breast sandwich, $6.50, or $6.95 with cheese. The clam chowder ($3.25 and $4.25) drew hearty praise from two diners next to us. Mexichili is $2.95 or $3.95. Salads range from $2.95 for a house salad to $7.95 for a taco salad with either beef or chicken, or the O'Hara's Caesar salad with steak tips. There is much, much more from which to choose, and there are always lunch specials as well.      The service here is very fast, considerate, informative and friendly. My Stalwart Companion chose the Chimichanga ($7.95), a flour tortilla filled to the brim with beef or chicken (she chose beef), refried beans, cheese, onion, and green chilies, then fried into a golden crispy brown packet. This is topped with a hearty serving of the Picante sauce, and sour cream. Alongside is a serving of refried beans and one of green rice (rice with fresh scallions). This is a very hearty, very delicious, not too picante-hot meal. So big, in fact, that half was taken home for super that evening.      I chose the Blarney sandwich ($6.50), from the Irish side of the menu. This is corned beef and swiss cheese on thick slices of marbled rye bread, which is dipped into beaten egg then grilled on both sides until crispy and the cheese inside has melted. On the plate was a dish of Thousand Island dressing for dipping. An unusual and delicious variation on the Reuben sandwich. Along-side was a thick, crisp slice of half-sour pickle, and a piping-hot mound of freshly hand-cut steak fries, which had been seasoned to perfection with a bit of salt and pepper and I think I detected a bit of hot pepper. These fries were super.      To drink we had a coffee and an iced tea, $1.50 each, and they were kept refilled without our asking. This ample and enjoyable lunch for two cost $18.67 with tax.      When in Brunswick stop by Pedro O'Hara's for a very good, if ethnically challenging, hearty meal. Eat! Enjoy! Ole and Begorah.