Joseph Papp, director of the Public Theatre in New York and Broadway producer, finds it virtually impossible to separate travel from his professional life. "I really don't take vacations," he admits with regret. "Every time I travel it's for a reason." There is always a writer to meet, a show to see and business to discuss.

Recently his wife, Gail, who heads the Public Theatre script department, insisted they take the QE2 to London for the filming of "Plenty." They were guests of the Cunard Line, which had been trying "for seven or eight years" to get Papp to lecture aboard ship about the theater. Though he describes the sailing as being "locked up for five days," Papp says he enjoyed his audience, avoided the telephone, "worked out every day in the very good gym" and jogged around the deck -- and agrees that the trip was a "sort of vacation."

Before shooting began for the movie, the couple drove across the moors and visited Penzance for the first time (Papp produced "The Pirates of Penzance" on Broadway). "That whole section of England is quite gorgeous." Then, after a week of filming in London, Papp went to Prague to deliver an Obie award to a Czech playwright, and then on to Moscow. There he visited with Soviet writer Victor Rozov, whose comedy, "The Nest of the Wood Grouse," Papp directed and is now presenting at the Kennedy Center; he arranged for Rozov to begin writing the screenplay.

Papp plans to return to the Soviet Union in April for six weeks to shoot the film, and then hopes to make a more extensive tour of the country. Among his favorite places are:

* Lower Broadway: "Because it has these great old iron buildings and the sun keeps hitting it in different ways at different times of the year. I love the streets of New York."

* London: "I fell in love with the country of Shakespeare. I seem to know so much about it, having produced all of his plays. The reference points are still there, and traditions still are very much alive."

* Hanoi: On a trip to Vietnam two years ago with American veterans to talk with government officials about MIAs, Amerasian children and Agent Orange, Papp enjoyed seeing the people and their culture. "Even the poorest carry themselves with a great deal of dignity. Tradition has not been disrupted."

* Cuba: Attending the International Theater Festival a year ago, he found it "like a little jewel physically, the weather is so beautiful. If it weren't for the political situation, and you looked at it objectively, it's one of the most beautiful islands in that area."

* Kodiak, Alaska: "When the flowers bloom in the spring, there are fantastic colors where you don't expect to see plants grow."