ON the historic occasion of entry into the United Nations, South Korea is out to show its best face to the world.Tonight in Carnegie Hall, followed by performances in Poland, Yugoslavia, Soviet Union, and Czechoslovakia (dates to be announced), 136 of the nation's top musicians, singers, and dancers will stage a cultural extravaganza of authentic costumes and choreography reaching back 5,000 years. With a combination of traditional and modern performances - known as court and folk traditions - the Ministry of Culture of the Republic of Korea is celebrating its UN membership that was announced on Sept. 17. "All the world knows about Korea is student demonstrations and turmoil they get from the media," says Sungyol Lee, director of Korea's Traditional Performing Arts Center in Seoul. "We want to show them our inner side, the wealth of our soul." Carrying an official message of global reconciliation, the tour is designed to introduce the finest organizations in the country - the National Traditional Music Orchestra, the National Dance Troupe, Kim Duk-soo samulnori (percussion) group, and the Seoul Art Company, among others. Long a point of contention between North and South, entry into the UN has been stalled by northern demands that the two share one seat. Bowing to international pressure after four decades, North Korea submitted a separate appl ication and was admitted last week as well. Despite demonstrators carrying placards outside Los Angeles's 6,000-seat Shrine Auditorium ("National Division is nothing to celebrate"), the capacity audience at the tour's premiere was reduced to both pandemonium and tears. The largest Korean population outside Asia helped pack the site of Hollywood's Academy Awards for an event that couldn't have been more un-Hollywood: 10 segments of highly ritualistic and ceremonial court music; epic dramatic narratives; a contemporary drum concerto for 40 players; a scarf dance; and ensembles 50-strong playing such otherworld instruments as the six-string komungo. "These are the finest performers in the nation who have dedicated themselves to preserving the essence of Korea's finest traditions," says Craig Coleman, executive director of the Korea Society. Two of the performers have been honored as "Human Cultural Treasures" by the Korean government: dancer Lee Mae-bang and singer Cho Sang Hyun. The program, entitled, "The Sound of Millenia," is divided into two fast-paced sections of 25 and 55 minutes. Part 1 is called "Meditation," and involves solemn ensembles of string and wind instruments. Part 2 is called "Great Joy," and utilizes drums and gongs in great flights of ecstasy. Forty players strike multicolored drums of all sizes while whirling like dervishes, shouting, and punctuating the air with synchronized gestures. The result was several spontaneous ovations, foot stomping, and dozens o f sobbing faces. As muscular and infectious as Moscow's Bolshoi Ballet, as otherworldly as China's Peking Opera, the performances are both strange and highly accessible. Though the music has no harmony, monotony is broken by vibrato that ranges nearly half an octave. Drum and dance rhythms are primitive yet undeniably energizing. As pure entertainment, the show is a visual and aural feast. Robust costumes add to fascinating choreography of hand and facial gestures - often executed by dozens of performers in unison. There isn't a dead spot in the performance. But as 60 pages of program notes, diagrams, history, and glitzy photographs point out, the Korean cultural tradition is far more than entertainment. Voluminous analysis and description explain such esoteric traditions as Buddhist monk dances, lyric opera known as "Chongak," and avant-garde theater that uses facial and hand-held masks in dualistic symbolism. Americans may scarcely fathom a tradition going back over 30 centuries, but a viewer is beguiled by its timeless majesty. The performers are out to distinguish themselves from the traditions of their Asian counterparts. "The range of yosung [vibrated sound] makes Korean music closer to that of India than either China or Japan," says Cho Sang-Hyun, a pansori artist. Pansori are poignant, sung narratives, often about love, family, departure, or reunion. The singers stand before an isolated screen, accompanied by a drummer. As the drummer maintains basic rhythm cycles, the soloist half sings, half recites while punctuating his song with dramatic gestures using a fan or handkerchief as a prop. First-time listeners will have to sort out such concepts as pentatonic and heptatonic scales (with different central tones and intervals). Spontaneity and humor often mitigate the inscrutable monotony and solemnity often associated with some Asian traditions. "Korean folk music bears witness to the ecstasy associated with folk religion," says Hyon-ung Shin, director of the Korean National Music Company. "We find we don't need a formal harmonic system, we find it [harmony] naturally." MR. SHIN says Korean music was influenced by Chinese music beginning in the 4th century, and it in turn influenced Japanese music by the 5th century. Folk music, known as aak, is derived from the yin and yang elements of five-elements theory. The five-tone scale, the arrangement of instruments and colors of costumes are evidence of the theory's influence. The hefty program is also a pictorial encyclopedia of drums, flutes, gongs, string and percussion instruments designed to engage audiences with a wealthy tradition. The only thing missing is a description of the uses of color: the variations of pinks, yellows, greens and blues; and costumes: the robes, pants, gowns, shoes, and headgear that are nothing like what Westerners know from Japan and China. "This has been a visit to everything glorious I remember of growing up in Korea," said one Korean audience member who left Seoul 17 years ago and now lives in the United States. "Everything I remember well.... Only better done than I have ever seen it."