Theme Cruises. Want to pursue your favorite hobby on your vacation? Solve a mystery, meet sports stars, hear hit songs from the big-band era, spruce up your golf game with help from experts -- all on board ship

IMAGINE discussing his latest book over dinner with James Michener while cruising around Asia aboard a Society Expeditions ship, talking global politics with former British Prime Minister Edward Heath while off the coast of England on a Royal Viking cruise, or listening to Helen O'Connell sing hits from the big-band era while sailing in the Caribbean on Holland America's SS Rotterdam. This year, cruise lines are offering an array of theme cruises to augment their normal itineraries. Theme cruises allow passengers to indulge a favorite hobby, learn a new skill, or meet an admired celebrity while enjoying an ocean voyage.

``My family is from Scotland, and I'd always wanted to see the castles here and learn about the clans,'' said Roger MacClaren of Chicago as we sailed into the harbor near Edinburgh on Royal Viking Line's ``Castles & Kings'' cruise around the British Isles last year. ``I was especially interested in the historical background they gave us.''

On other theme cruises, sports fans can meet their favorite football or hockey players, music lovers can hear evenings of opera, and amateur sleuths can solve a mystery. Cunard is offering a five-day mystery cruise from New York to Bermuda on the Queen Elizabeth 2, sailing next Monday.

``The mystery actually begins at the pier,'' explains Cindy Kampf, a Cunard Lines spokeswoman, ``and the suspects [actors masquerading as real passengers] get on board with the other travelers. Then during the course of the voyage, a `murder' takes place, and the passengers try to figure out who did it.'' By the time the ship docks in Bermuda, the mystery will have been solved, and on the return voyage to New York, passengers hear lectures by real-life detectives and old-time radio mystery personalities.

Other Cunard theme programs include hockey and baseball cruises in the Caribbean, a September ``Travel Photography'' cruise aboard the Sagafjord, also in the Caribbean, and an archaeology cruise on the Vistafjord in the Mediterranean. The Queen Elizabeth 2's ``Baseball Hall of Fame'' cruise in October will feature legendary figures such as Willie Mays, Yogi Berra, Brooks Robinson, and Ralph Kiner.

Norwegian Caribbean Lines (NCL) is offering a variety of themes on its fall and winter seven-night cruises in the Caribbean. Fall sports cruises will feature such tennis experts as Omar Fareed and Kathrin Keil; basketball greats Dave Cowens, John Havlicek, and Sam Jones; golf pros Mary Beth Zimmerman and Tom Shaw; and ski experts Kiki Cutter, Christin Cooper, and Jimmie Heuga. In addition to giving talks and meeting with the passengers, the sports stars all participate in special on-board ``Olympics'' competitions and give lectures or demonstrations.

Norwegian Caribbean also offers a November fitness and beauty cruise, with a television fitness expert, Sheila Cluff, as hostess. ``The cruise offers a relaxed environment in which people can start an exercise program,'' says Miss Cluff, who owns two fitness spas in California. ``The week-long cruise will get them started on a program they can then follow when they get off the ship.'' Workshops on beauty, skin and hair care, and nutrition will be given on this cruise, as well as lectures by sports celebrities. Passengers can also participate in workout sessions with Olympic athletes.

While most cruise lines simply add theme cruises to their regular itineraries, Royal Viking Line actually plans many of its itineraries around the themes. Royal Viking's ``Pacific Memories'' cruise, for instance, sails in March through the South Pacific and includes stops at the sites of battles and staging areas of World War II. Movies, lectures, and special programs relating to the theme are presented on this cruise, which is popular with World War II veterans.

Alaura Crank of Beverly Hills, Calif., was a passenger on Royal Viking's ``Connoisseur's Europe'' cruise, which sailed in the Mediterranean and allowed passengers to sample the culinary pleasures of Barcelona, M'alaga, and the Bordeaux region of France. ``We ate in wonderful ch^ateaux and in little French villages,'' remembers Ms. Crank, ``and a Swiss chef came on board to give a lecture and cooking demonstration. Everything had to do with fine dining. It was a wonderful experience.''

Royal Viking's ``Worldwide Golf'' cruises enable passengers to play on such celebrated courses as Princes Street Gardens in Edinburgh; Gleneagles in Auchterarder, Scotland; Mahogany Run on St. Thomas; and the New South Wales Golf Club in Australia. Voyage Home cruises to Northern Europe take passengers to the line's Scandinavian homeland, where talks and programs are given about Norwegian customs, history, and folklore.

The ``Celebrity All-Star Band Salute'' on Holland America's Rotterdam in the Caribbean this fall will feature jitterbug contests and Dixieland jam sessions, as well as swing-era greats Helen O'Connell, John Gary, Connie Haines, and Dennis Day, singing with the Roger James Big Band. January sailings on Sun Line Cruises' Stella Solaris to the Caribbean, the Panama Canal, and Latin America will feature Billy Eckstine, Joe Williams, and the Harlem Blues and Jazz Band.

This fall and winter, Western Cruise Lines' Azure Seas will offer a ``Star Trek'' cruise, featuring celebrities from the popular television series, and a '60s cruise with Glenn Yarbrough and the Limeliters. Eastern Cruise Lines' Emerald Seas will have Country Music cruises starring George Strait, Conway Twitty, Johnny Lee, and Lane Brody & Thom Bresh.

Theme cruises may not be for everyone, however. Marian Grace of San Francisco took an opera cruise on Royal Viking last year and was disappointed. ``I was raised on the Metropolitan Opera music, and I've studied and sung opera myself,'' she says, ``and the operatic presentations on the ship were not up to par. It was a superficial look at opera. I'd expected more.''

Although not typical theme cruises, nature-study trips are offered by smaller lines such as Exploration Cruise Lines and adventure travel companies such as Society Expeditions and Special Expeditions. They can be some of the most successful cruise programs. Exploration Cruise Lines has a fleet of small (50 to 250 passenger) ships that sail to remote areas of Mexico, Tahiti, Alaska, and Baja California and go into tiny inlets and narrows to observe wildlife. You can watch harbor seals and killer whales in Alaska, or study elephant seals and exotic lizards in Baja California.

Society Expeditions' trips to Antarctica are led by naturalists and concentrate on observing the environment. Special Expeditions cruises around Baja California give adventurers the chance to touch the ``friendly'' gray whales and learn, from experts, about the unspoiled waters of the Sea of Cortez.