For all the changes wrought on both sides by the opening of the borders between East and West Germany, it seems to have affected the character of Kissinger Sommer scarcely at all.

But then this annual summer festival, which just completed its fifth season, has always partaken about equally of East and West. Artists, whether musical, dramatic or graphic, are as likely to come from such once-remote spots as Czechoslovakia and the Soviet Union as they are from Western Europe and the United States.That mix was evident again this year as the festival wound up a 31/2-week run July 15. (Courtesy of Lufthansa and the festival itself, we caught the last three days on our way to Weimar.)

On consecutive nights one could hear not only an East German string quartet but a Bach cantata program using Eastern players and Western singers and a concert that sported a Russian-born soloist (Israeli violinist Shlomo Mintz), a Romanian-born conductor (Atlanta Symphony music director Yoel Levi) and a West German orchestra, the Bavarian Radio Symphony.

(Earlier programs had offered, among others, the Polish Radio Symphony, Hungarian pianist Dezso Ranki, American cellist Lynn Harrell with the Czech Philharmonic, Dresden's Musica Viva Ensemble under composer Udo Zimmermann, West German mezzo Waltraud Meier and, by way of Czechosolovakia's Theater on the Thread, newly elected president Vaclav Havel's play "The Garden Fest.")

The result was a three-for-three average any festival might envy.

If there is a group around with a tighter sense of ensemble than East Berlin's Petersen Quartet, I have yet to hear it. Whether in string quartets of Boccherini, Mozart or Shostakovich, performances were exquisitely balanced, with an inner tension that kept things light without diminishing their energy. Indeed, the finale of the Mozart, the K. 387, fairly leapt from the page.

Occasionally more bite would not have been amiss in the Shostakovich, the familiar Eighth Quartet. But this, too, made its points, from the quietly searing second section to the lyrical sadness of the finale.

Adding to the atmosphere was the fact that this concert was presented outdoors, in the "jewel court" of the Regentenbau, with its Grecian statuary. Similarly taking advantage of the balmy weather, the following evening's Bach program was likewise an open-air affair, amid the food-and-drink-laden tables of the inner court of the Luitpold Casino.

That proved an agreeable venue for such cheerfully secular fare as the "Coffee" and "Peasant" Cantatas, which profited additionally from the characterful singing of soprano Ruth Ziesak and bass-baritone Andreas Schmidt and the lively work of Leipzig's New Bach Collegium Musicum under Burkhard Glaetzner.

Certainly both singers were alive to the mock seriousness of the "Coffee" Cantata, aided by tenor Hans Peter Blochwitz. But the stylishness of the playing was equally welcome in the "Peasant" Cantata; ditto Ziesak's skillful pointing of both the music and the text.

The beautiful-sounding, wood-paneled interior of the Regentenbau was the setting for the final concert, for which Levi served up a program as international as the artists: Barber's "School for Scandal" Overture, the Tchaikovsky Violin Concerto and Bartok's Concerto for Orchestra.

Although one of Germany's finest, the Bavarian Radio Symphony does not match the precision of its American counterparts in the Barber. But the warmth and athleticism of its accompaniment in the Tchaikovsky made an interesting foil for Mintz's compellingly old-world view, its texture and tone varied in unexpectedly personalized fashion.

Likewise the Bartok, its European colors brought out in a way one seldom hears in this country, for all the tautness of Levi's direction. Yet apparently not European, or at least traditional, enough, for if there were any complaints about this year's festival they centered around what many perceived as an undue emphasis on "contemporary" music.

"Why did he choose to end the festival with Bartok?" more than one person was heard to ask at the concert's close - this of a piece one would have thought had been accepted as part of the musical mainstream long ago. Yet that same traditionalism contributes to the special character of both the festival and this northern Bavarian resort town.

At no other festival known to me is one as likely to encounter old friends - this year, for example, three-fourths of the critics were returning critics - and that extends to the town itself. Relatively isolated, its intimacy and charm are unique in an increasingly Westernized West Germany. For example, McDonald's may be in Moscow but they haven't yet penetrated to Bad Kissingen, where one precedes a concert not with a Big Mac but, if he wishes, with a stroll in the gardens and yet another open-air pops program.

One of our luncheon hostesses, we discover, is the daughter of Kaiser Wilhelm II's personal physician. At the same time young people are evident not only in the audiences but among the performers, most dramatically in a Sunday-morning concerto program highlighting the artistry of the 9-year-old German-American violinist David Garrett.

I find myself thinking I have heard less imaginative accounts of the Mozart K. 219 Concerto from soloists four and five times his age. In short, he played the pants off it, with some real fireworks in the finale. Yet in true Kissingen fashion, his reward, other than the applause, combined the old and the new - a medieval-dragon puppet presented him with a special gift, a miniature racing car.

By the same token a stroll into the old town the preceding morning brings another unexpected concert, by a high-school marching band whose final numbers bring down the house: "When the Saints Go Marching In" and "The Battle Hymn of the Republic." Or might that be, of the German Federal Republic?