Sauté is a cooking technique that requires the use of a large amount of heat for a small amount of fat in an open pan, and allowing the food to become brown and form a crust, and not to the extent that it will stick to the pan as it cooks. Regardless of the nature of the stove, you're using, what is important is that you use a high flame. The common fats for this process are oil and butter. As for stir fry, which is also a cooking technique, it involves the use of a larger amount of heat compared to the amount used in sauté, and also, a larger amount of fat.
Unlike in sauté, where the common fats are oil and butter, oil is used more often than butter in the stir-frying cooking technique. Another difference you would notice is that both use different types of cooking pans. The common type of pan for sautéing is sautéed pan, whereas the common type of pan for stir-frying is a wok.