Since 1968, the Music Festivals at Sea, which Paquet Lines of France sponsors twice annually on the MS Mermoz - January in the Caribbean, September in the Mediterranean - have offered not only visits to exotic ports of call, but a varying and formidable cargo of distinguished performing artists. In fact, when he read the roster of last January's Caribbean cruise, a noted American conductor exclaimed in mock terror, ''If that ship should vanish, it would be the end of music!''
For years, such international names as flutist James Galway, cellist Yo-Yo Ma , pianist Emanuel Ax, trumpeter Maurice Andre, and the English Chamber Orchestra have confidently reserved time in their busy concert schedules to join familiar colleagues and new musical acquaintances on the Mermoz in what for them is a continuing artistic adventure - improvising, experimenting, and making music for a built-in, receptive audience in the relaxed atmosphere on board ship and in carefully chosen performing sites ashore.
For the musically oriented passenger, the festival is a unique combination of concertgoing and sightseeing, as well as a rare opportunity to meet and talk with performers as friends and travel companions. The artists invited to participate in the cruises by impresario Andre Borocz are ''great,'' but not the kind who demand kid-glove treatment.
From the moment one boards the Mermoz, everything has been arranged, and a Ship's Daily Journal, placed under each stateroom door early in the morning, lists the day's multiple choices, musical and otherwise.
Since the Mermoz is a bilingual ship, each full day-at-sea schedule provides ''flash excursion'' travelogues in both English and French about the next port to be visited. There are Music Magazine talks, with audience and artist participation on many musical subjects - in English by Karl Haas (of WQXR in New York), a radio commentator whose daily syndicated ''Adventures in Good Music'' reaches millions of listeners worldwide; in French by Claude Lehmann, eminent French musicologist and critic. And in the afternoon, new films, often with musical subjects, are shown in the ship's submarine cinema. In the record shop, autographing of recordings by shipboard personalities allow for face-to-face questions and conversations.
Rehearsals in the lounge are business as usual for musicians - and open to passengers, who may come and go without disturbing these working sessions. Although their musical paths had crossed before, soprano Barbara Hendricks and cellist Yo-Yo Ma had never performed Schubert's ''Shepherd on the Rock'' together. Since the instrumental part is most often played on the clarinet, we were fascinated at rehearsal to hear the singer, pianist Marielle Labeque, and the cellist diligently gauging tonal balances and phrasing in this unaccustomed version with strings replacing reed sound. What a pleasure to experience the exquisite result at Miss Hendricks's lieder recital the next night.
A larger group, consisting of Marisa Robles, the Spanish harpist, flutist James Galway, clarinetist Gervase de Peyer, and the Czech Panocha Quartet, was able to put together a memorable performance of Ravel's ''Introduction and Allegro.'' It was an ideal selection to accompany tropical waves and bright-burning southern stars.
Music cruises on the Mermoz have a great many repeaters, among both passengers and musicians. If you ask them why they keep coming back, they are often at a loss for an answer. For the nonperformer, it is often the experience of hearing music free of going to concert halls and the fellowship with the artists and other equally enthusiastic listeners.
For the artist, the Mermoz is a haven for performing, sightseeing, and remaining reasonably free from close plane connections, frantic fans, and vapid interviews. Here, listener and performer treat one another like ordinary people who have the same abiding interest and feel no need to explain why.
On days when the Mermoz comes to port, the schedule accelerates. We couldn't miss being up on deck early, for instance, as the ship approached Curacao harbor to watch the unique Queen Emma pontoon bridge swing open to let us pass. Then, as our floating home proceeded up the canal-like channel to its docking area, we could almost reach out and touch the colorful toy-town row of Dutch houses on Willemstad's waterside street, the Handelskade, an Amsterdam in miniature. Of the ports visited during last January's Caribbean trip, Curacao is the only one the Mermoz will repeat on the 1984 Music Festival at Sea.
The day ashore includes shopping, sightseeing, and perhaps sampling some of the tropical fruit at Willemstad's floating market with its flotilla of small boats that arrive daily with fresh produce from Venezuela. Some non-rehearsing musicians join us on our rounds, but by 5:30 p.m. everyone is back at the Mermoz pier ready to be transported by buses over the high, fixed bridge named for Queen Juliana of Holland, with its spectacular bird's-eye view of the island and Schottegat Bay, seventh-largest harbor in the world.
Arriving at Curacao's modern Pro Arte Center for the evening concert, we were welcomed by Curacaoans serving refreshing fruit drinks and crisp pastries before the program, which featured no less than Miss Hendricks singing Mozart, Yo-Yo Ma playing a Haydn concerto, and Paris Opera dancers Francoise LeGree and Michael Denard in a Bejart ballet, all with the assistance of the 27-member English Chamber Orchestra. Then back to the ship, where an accurately named buffet magnifique is served at 9 p.m. on the grill deck with Willemstad's forest of lights blazing on shore.
Each port, each concert, and indeed each day at sea surprises us with as many unexpected variations as Bach, Beethoven, or Brahms could ever have dreamed of.
Who wouldn't be delighted after hours of sightseeing, feasting, and music to linger in the lounge late in the evening and hear a ''pickup'' group including James Galway, pianist Emanuel Ax, violinist Yuko Shiokawa, and Yo-Yo Ma put a spirited end to the day with an extempore version of the ''Eroica'' Symphony? Or remark with wonder how the tree frogs stilled their chorus when Hans De Vries played a Bach concerto for oboe d'amore with the chamber orchestra in the darkening courtyard of the Barbados Museum?
Everyone goes home with special memories compounded of sight and sound, land and sea, and the universality of music and its adherents.
The Mermoz Music Festivals at Sea go on this year through Sept. 14 in the Mediterranean, and in the Caribbean from Jan. 31 through Feb. 12, 1984. On this latter, 25th cruise, the Mermoz, sailing from San Juan, P.R., will visit Martinique (Fort-de-France), St. Vincent (Kingstown), Trinidad (Port of Spain), Curacao (Willemstad), Santo Domingo, and Haiti (Port au Prince), with five days at sea interspersed, before returning to San Juan.
Mstislav Rostropovich, the celebrated cellist-conductor-pianist; his wife, soprano Galina Vishnevskaya; and their daughter, pianist Elena Rostropovich, are already announced to return for the 1984 Caribbean Music Festival in January, along with James Galway, Maurice Andre, and violinist Shlomo Mintz. Pianist Malcolm Frager will join the artists roster for part of the 1984 trip. Chamber groups from Budapest and Norway and other musicians yet to be announced will be also be on board.
Prices for the 12-day Caribbean Music Festival - which include all concerts on sea and land and everything except such personal expenses as hairdressers, laundry, cleaning, and boutique purchases - range from $2,865 to $5,045, with deluxe accommodations reaching $6,315. There is free roundtrip air transportation to and from San Juan from most United States cities, and special rates for a third or fourth person sharing a cabin. The Mermoz, named for the French aviator-hero, Jean Mermoz, has been in service as the music festival ship since 1976.
Complete information about the forthcoming 1984 music cruise is available from Paquet Cruises Inc., 1007 North America Way, Miami, Fla. 33132. Telephone ( 305) 374-8100.