Pepsico's profit rose 25% to $190 million in the third quarter. The Purchase, N.Y., soft-drink and fast-food concern said part of the increase was from the purchase of Kentucky Fried Chicken in October, 1986, which led to a 73% climb in restaurant earnings. The company also owns the Pizza Hut chain. Soft-drink earnings rose 16% on a sales increase of 9%. The company attributed the gain to higher profit margins and double-digit gains in sales of Diet Pepsi and Mountain Dew. Snack foods, which include Fritos corn chips and Lays potato chips, recorded a 23% rise in earnings on a 7% gain in sales. Total revenue for the quarter was up 26% to $2.94 billion.