THOUGH the raga has been widely popularized in the United States in recent years, thanks to its introduction by Indian musicians Ravi Shankar and Yehudi Menuhin, a great unfamiliarity with the art as it is actually practiced in India still exists.

Sitarist Mahunud Mirza, the first major artist of the Kirana school to appear in this country, intrigued and delighted a sparse Spingold Theatre audience Saturday night with a fascinating demonstration of his sitar virtuosity.

Mirza mesmerized the crowd with his facile dexterity in unfolding two highly complex ragas, creatively exploiting each musical possibility of variation. He maintained a self-assured quality of coolness throughout the performance, interpreting difficult thematic material with graceful case, suggesting deceptive simplicity.

Mr. Mirza's sitar seemed to wail out emotion in a vocal idiom characteristic of the centuries-old Kirana school in which he was trained. While other schools of sitar-playing emphasize greater instrumentality, Mirza's "singing sitar style offers a welcome depth of feeling to the western listener who has difficulty intellectualizing the sophisticated raga system.

Like American jazz, the Hindustani music of India is improvisational. The raga is the mode or theme on which the performer improvises spontaneously, developing 95 per cent of the piece originally. It is an unwritten, oral tradition that has been handed down through the generations since about 1500 B. C.

"Within the limitations of a very systematic set of rules, are found all the elements of emotionality and relevance," explains Mirza. "You can begin anywhere, but once you start, you have to dive into yourself."

Mirza's ragas show a clarity that American critics have often found lacking in performances of other Indian musicians. He manages to achieve organic union of his melodic material with the complementary rhythms of his tabla accompanist Faygaz Khan, without sacrificing the hold definition of the raga's theme.

During the "gat" phase when the raga is set to a sixteen-beat rhythmic time cycle, and during the speeding climax of the "thala," there appears to be a heightened intensification-rather than a confusion-of the raga's mood, as Mirza and Khan seem to mysteriously coalesce in a musical vision of sheer symmetry.

The raga's path seems to change on the first beat of each cycle, which acts as a convergence point for the interplay of the two instrumentalists. Mirza sometimes suggests a rhythm in his strumming, picking right hand (the lute-like sitar is played vaguely like a guitar) which Khan then develops more fully during the coming cycle.

At other times, Khan pursues a new, syncopated tempo, while Mirza takes the first note as a starting point for "bending the pitch" of the next interval, to be played in "meend," a technique similar to the "blueing" of notes in jazz. "The beauty of the sitar lies in pulling the notes from one fret to another," according to Mirza. The drawn-out sounds create the strange, modal, wailing effect which western ears find so intriguing.

"THE BEATLES did a great deal for sitar music, but they knew nothing about it," Mirza told me last week. "They exploited it for the pop mania. There has been a great sinking of Indian music in the United States during the last year because of its commercialization and exploitation. Trying to cater to all tastes like a very bad cook has been responsible for its demise from interest."

But Mr. Mirza made no attempt to simplify his usual playing style to suit his culturally-distant American audience last Saturday, and his unassuming honesty-coupled with his virtuoso elegance-was received with great enthusiasm. The small size of the audience permitted a certain intimacy which provided the atmosphere in which Indian music was meant to be heard. The Brandeis listeners probably sensed little of the Hindustani culture in which the raga is firmly rooted, but they undoubtedly came away with a feeling for the romantic delicacy of Indian music well-performed.