IF it's Thursday, it's Saquisili. If it's Saturday, it's Otavalo.For either town, it is market day, when Ecuadorian Indians pour out of the Andes foothills to bargain, buy, and trade. The streets and squares bulge with stout, short men and women in porkpie hats and red or dark ponchos, selling anything from squealing pigs to bars of soap to brown rice in sacks. Many of them have arrived on bare feet carrying enormous rope-bound bundles on their backs. Others come wearing shoes and pushing homemade carts; they bring food, utensils, folding chairs, and homemade grills to roast and sell goat meat, beef, ham, and wonderful-smelling soups. The tour books say Otavalo and Saquisili are the two most important Indian markets in Ecuador. The origins of each stretch back to pre-Incan times. If visitors don't arrive between 9 and 11 a.m. they'll probably miss the height of the serious transactions. Men look for pants, shoes, rope, and tools. Women, already wearing beautiful embroidered blouses, need vegetables, herbs, flour, and clothes for children. At Otavalo most of the men plait their black hair into a single braid down their back. Outside town, the animal market is over quickly. Black pigs are sold, along with sheep painted with purple X's to indicate slaughter; here, too, is grass for Panama hats (real ones are made in Ecuador) and trucks piled six high with helpless sheep, a sight to make animal activists cringe. After the morning rush, the rest of the day is just as thickly packed, but slower paced. Touristas arrive and wander around with sucres to spend on woven baskets, sweaters, and rugs made from sheep and llama wool. No noisy bargaining or yelling here, although you never stop at the asking price. This is bargaining more as a social exchange, but not too social. Occasionally, a broad smile when an exchange is complete will include the flash of a gold tooth.