Heat oven to 350°F. In ungreased shallow pan, place walnuts. Bake 6 to 10 minutes, stirring occasionally, until light brown. Cool 5 minutes.
Finely chop 1/2 cup of the walnuts. Spread on sheet of waxed paper; mix with oregano.
In food processor, place cream cheese, feta cheese and mayonnaise. Cover; process with on-and-off pulses 20 to 30 seconds or until well mixed. Add olives and remaining 1/4 cup walnuts. Process by pulsing 4 or 5 times until chopped and mixed. Cover and refrigerate about 1 hour or until firm enough to shape into balls.
Using 1 teaspoon for each, shape cheese mixture into 60 balls. Roll in walnut-oregano mixture to cover. Place in tightly covered container. Refrigerate about 1 hour or until firm. Serve with pita chips.