A TRIP to the European festivals is at best a voyage of discovery, seeking not just music, theater, films, dance and art galleries, but the very things that make the festivals different in different places: the people, the architecture, the history, the food and drink, the scenery, the very flowers.

This year, more than 50 music festivals alone deck the European map, stretched out from April to October, from Aix-en-Provence to Zurich. It would take a tireless traveler with seven-league boots to visit them all, but traveling only by train, car or bus, you can make it to some in a single circuit.

If you can possibly manage such a trip, don't let anyone talk you out of it. With luck, you will have a wonderful time and be enriched forever when the curtain falls. Although it's not a good idea to tie yourself down to an inflexible schedule, it is wise to make your plans foolproof at the festivals where reservations can be hard to come by. But between festivals and festival performances, wherever a place looks enticing, go there if you can.

A car is ideal for festival junketing, though train and bus are cheaper if you are traveling alone. With a car you have more freedom, and in Europe you don't have to drive for days to get where you want to go. From Salzburg to Verona you can explore the corkscrew mountain passes of the pink-crystal Dolomites. From Paris to Aix-en-Provence you can meander leisurely through the chateau country of the Loire.

Whichever routes you choose, here is a guide to this year's festivals, with dates and some details to help in the planning.

AIX-EN-PROVENCE, France, July 21-Aug. 2. A stately old city in the heart of Provence with a chic festival atmosphere. Few thoroughfares can match its Cours Mirabeau in the lofty shade of four great avenues of trees. It has beautiful fountains and old houses with exquisite gardens. Concerts spill over into lovely courtyards and cloisters, with opera in the courtyard of the 17th-century archbishop's palace. Operas this summer include such offbeat items as Mozart's "Mitridate, re di Ponto," Rameau's "Hippolyte et Aricie" and Rossini's "La Cenerentola."

ATHENS, Greece, June-September. Greek drama and modern theater, plus opera, concerts and ballet, all in open-air performances in the ancient Odeon of Herod Atticus and at the Lycabettus Theater.

BARCELONA, Spain, Oct. 1-31. Orchestra and chamber music concerts, early music and oratorios, plus recitals. Catalan music is a focus this summer.

BATH, England, May 27-June 12. Monteverdi Choir and English Baroque Solists. Gyorgy Pauk and Peter Frankl in violin-piano recital, string quartets from the Amadeus to the Alberni groups.

BAYREUTH, West Germany, July 24-Aug. 27. This ugly, sizzling, comfortless town is the site of the Wagner house on the hill, which still attracts tailcoats and trailing satins at 4 in the afternoon, and clings to uncut performances of Wagner's operas in an acoustical marvel of a theater designed by the composer himself. Wolfgang Wagner, a grandson, is still in charge, and nowhere will you find Wagner's operas more spectacularly staged. This summer marks the 100th anniversary of the composer's death in Venice with a new production of "The Ring" cycle, directed by Peter Hall of the Shakespearean stage, and conducted by Sir Georg Stolti.

"Meistersinger," "Parsifal" and "Tristan" are also listed, but most performances of "The Ring" are already sold out.

BERGEN, Norway, May 25-June 8. Opera, drama, ballet, concerts in the homes of Edvard Grieg and Ole Bull. Jazz, folkloric and children's events and exhibitions.

BERLIN, West Germany, Sept. 2-Oct. 30. 33rd Berliner Festwochen, featuring the Berlin Philharmonic under the direction of Herbert von Karajan, plus other orchestras, and three days of jazz concerts.

BESANCON, France, Sept. 2-5. Competition for your conductors, with visiting orchestras, chamber music and recitals.

BRATISLAVA, Czechoslovakia, Sept. 30-Oct. 14. Wide range of Eastern European orchestras and "International Rostrum of Young Concert Artists," in cooperation with UNESCO.

BREGENZ, Austria, July 21-Aug. 21. Cole Porter's "Kiss Me Kate" on the floating stage on Lake Constance. Weber's "Der Freischuetz" in the Festipielhaus -- a production designed by Otto Schenk. Solosits with orchestra and in recital include Hermann Prey and Mariella Devia. Not far away is Oberammergau of the Passion Play.

BUDAPEST, Hungary, July-August; Sept. 25-Oct. 27. Mid-summer chamber music and chamber operas in the castle district, contemporary music and opera in the fall.

DUBROVNIK, Yugoslavia, July 10-Aug. 25. The medieval city, which glitters like white ivory in the night, has 46 open-air stages and boasts 110 performances each summer, ranging from folk dances to Eastern European opera and ballet.

EDINBURGH, Scotland, Aug. 21-Sept. 10. The bravura city, the jagged castle rock, the royal mile to Holyrood, the military tatoo. You can always count on major operatic productions, front-rank orchestras and stellar recitalists.

FLANDERS, Belgium, in progress through October. Commemorative concerts concentrating on the music of Frescobaldi, Soler and Rameau in a wide range of cities, from Bruges to Ghent to Limburg and Antwerp. Richard Strauss' "Capriccio" with Kiri Te Kanawa as the lady in the case.

FLORENCE, Italy, May-July. Major operatic and symphonic concerts, ballet and chamber music. Ricardo Muti conducts.

GRANADA, Spain, June 20-July 7. Dutch Chamber Orchestra with Teresa Berganza as soloist, the National Orchestra of Spain led by Jesus Lopez Cobos, among others, London's Royal Philharmonic conducted by Uri Termirkanov and the Scottish National Ballet.

GRAZ, Austria, Sept. 11-Oct. 23. Concerts and symposiums concentrated on contemporary music and theater.

HELSINKI, Finland, Aug. 25-Sept. 9. Finnish Radio Orchestra and other symphonic ensembles. Music by Sibelius, Saalinen and standard fare.

HOLLAND FESTIVAL, May 15-Sept. 4. A moveable feast of music, from Rotterdam to Amsterdam to The Hague and Utrechet. Mozart's "La Clemenza di Tito," music by Schoenberg, Stravinsky and Hindemith. The Netherlands Dance Theater and Dutch National Ballet.

ISTANBUL, Turkey, June 20-July 15. Performances of everything from Turkish folk music to opera and modern dance in Byzantine and Ottoman sites, and open-air theaters.

LINZ, West Germany, Sept. 4-Oct. 2. International Bruckner Festival, featuring the Bamberg Symphony, Cracow Philharmonic, Orchestra de Paris, with Anne-Sophie Mutter, Christa Ludwig, Alexis Weissenberg and others.

LJUBLJANA, Yugoslavia, June 2-Aug. 30. Orchestras, opera, ballet, plus puppet shows and folkloric exhibits. Symposiums and the 10th Yugoslav Ballet Biennial.

LUCERNE, Switzerland, Aug. 17-Sept. 10. The Kunsthaus near the Lake is the site for most of the festival's major concerts, focusing on Wagner and Brahms this summer. The Dresden Staatskapelle, Israel and Berlin Philharmonics, and Amsterdam Concertgebouw are among the visiting orchestras.

LYON, France, June 6-30; Sept. 18-28. Berlioz's "Romeo and Juliet" in June, his "The Damnation of Faust" in the fall.

MONTREAUX-VEVEY, Switzerland, Aug. 27-Oct. 2. Major orchestras, including the Leningrad Opera Orchestra, plus such noted artists as Yehudi Menuhin and Mstislav Rostropovich. concerts in castles and churches.

MUNICH, West Germany, July 8-31. Munich always has superior opera. The repertory is inquisitive these days, with less concentration on Strauss. New productions this summer of Wagner's "Rienzi," Purcell's "Dido and Aeneas" and Monteverdi's "Il Combattimento di Tancredi." Schoenberg's "Moses and Aron" will be repeated from last summer's list.

PRAGUE, Czechslovakia, May 12-June 4. Czech Philharmonic, the Moscow and Berlin Philharmonics, the Prague Symphony Orchestra, the Lyon Symphony, with soloists including Mirelli Freni, Peter Schreier, Garrick Ohlsson, Alicia de Larrocha, and more.

SALZBURG, Austria, July 26-Aug. 30. Mozart's town, and Herbert von Karajan's. Always alluring opera, this year new productions of Strauss' "Rosenkavalier" and Mozart's "Idomeneo." James Levine, Lorin Maazel and Riccardo Muti conduct, Placido domingo sings zarzuelas in concert with Pilar Lorengar. Soloists include Vladimir Ashkenazy, Edita Gruberova and Bruno Leonardo Gelber.

SANTANDER, Spain, July 11-Aug. 31. Beethoven's "Fidelio" is the featured opera, the U.S.S.R. Radio and Television Orchestra makes an appearance, Elene Obratsova and Montserrat Caballe sing, Italy's I Musici pays a visit.

SPOLETO, Italy, June 22-July 10. Ken Russell's new production of Puccini's "Madama Butterfly" bows, plus another new production of Samuel Barber's "Antony and Cleopatra." The Eliot Feld and Australian Ballets are among the dance groups listed. Recitals and concerts abound. The Umbrian hilltown is the chief delight, though, with ancient byways and truffled cuisine.

SOFIA, Bulgaria, May 24-June 21. Sofia Philharmonic, the New York Philomusica and Scottish Chamber Orchestras play, along with the Belgrade Madrigalists and Swiss, German and Russian ensembles.

STRASBOURG, France, June 10-25. Brahms' "German Requiem" will be mounted in the old cathedral, the Strasbourg Philharmonic, Zurich Chamber Orchestra and Bamberg Philharmonic perform. Rameau's rarely-heard opera, "La Guirlande," turns up in a new production.

STRESA, Italy, Aug. 25-Sept. 25. Chamber music is rampant, from the Trio di Trieste to the Cologne Chamber Orchestra and the Soloisti di Zagreb. Henryk Szeryng, Menuhin, Nikita Magaloff and Zubin Mehta with the Israel Philharmonic are among the stars.

VERONA, Italy, July 7-August. The Roman arena is quite a setting no matter what operas are mounted. The stage is 250 feet wide and the audience numbers more than 25,000. But you can hear and see, and when night falls, those in the circling tiers light candles. The neaby Due Torri is more like a palatial private house than a hotel. This summer the fesitval reverts to its traditional "Aida" and Puccini's "Butterfly" and "Turandot." Try delicious peach ice cream at Savoia's across the Piazza Bra, or eat delightfully across from the arena at the Tre Corone Cafe.

VIENNA, Austria, May 7 -- July 19. Donizetti's "Viva la Mamma" debuts and continues in 37 performances, "Turandot" will have yet another revival, with chamber music galore to accompany the Sacher Torte washed down at Demel's in the Kohlmarkt with Viennese coffee and whipped cream.

WARSAW, Poland, Sept. 16-35. International Festival of Contemporary Music. The latest in electronics and avant-garde fare, ranging from concerns to operas.

WROCLAW, Poland, Sept. 1-7. Another Polish festival, this one forcused on oratorios and cantatas, with visiting groups from Holland, Germany, Bulgaria and Britain.

ZURICH, Switzerland, end of May to early June. Verdi's "Aida" gets fresh treatment at the opera, the Tonhalle concert hall holds concerts conducted by Maxim Shostakovich, Wolfgang Sawallisch, with Christoph Eschenbach, Claudio Arrau, Maurice Andre and Gidon Kremer among the soloists.

For more program details, borchures and tickets to these fesitvals, wirte the European Association of Music Festivals, 122 Rue de Lausanne, Geneva, Switzerland. For information about the Spoleto Festival, which is not a member of the association, write c/o 609 Fifth Ave., New York, N.Y.