Phyllis Diller, who will be appearing at Wolf Trap next Friday night as part of a George Gershwin evening, describes her entire life as one big vacation. However, sometimes the comedian goes on "working vacations" when she makes guest appearances on TV talk shows around the country and answers mounds of her fan mail in between playing tourist. "A real vacation is when I don't take all my papers with me. The stacks of my material and other work all stay home."

Diller lives in Brentwood, Calif., a Los Angeles suburb, and New York City. After 28 years in show business, she likes to get away from it all with a visit to a Western dude ranch or an isolated beach in Bermuda. Her favorites include:

* IXL Ranch, in Sheridan, Wyo.: "The letters stand for Ninth Lancers Regiment. This is a huge ranch which a friend of mine owns. You sit there all day in this fabulous country club setting with mountains that act as a backdrop against blue skies and little puffy white clouds. I can go swimming, horseback riding and play tennis. My friend raises buffaloes there and he promised me his first-born buffalo will be named Phyllis (if it's a girl) and Mr. Phyllis if it's a boy. It's all very private and wonderful."

* Bermuda, and Nassau, Bahamas: I have friends in both of these places and they usually take me around the islands. I can play tennis, swim and sail when I'm there. Going to Paradise Island near Nassau was one of the greatest trips of my life."

* Mackinac Island: "This is off the coast of Michigan. It's just like a movie set. The hotel there is more than 100 years old . . . and there are no cars on the island. I was picked up at the airport in a horse-drawn bus that was in mint condition and the man driving me was dressed in full English livery. Everyone there either rides a bicycle, horse or walks around. It's just like a time warp."

* Canada: "I really love going to Canada. The people are very polite--they're not apt to jump you like here in the United States . Toronto is a wonderful place with a lot of fine hotels and good shopping. I played Edmonton-Calgary once in the dead of winter when the snow was piled up to the ceiling. I kept warm with many fur coats."