Nearly 300 young musicians from over 60 countries of the world have descended on Moscow for the month of June to compete for prizes in what may be the most prestigious of all musical contests, the Tchaikovsky Competition.

Inaugurated in 1958, when an unheralded and virtually unknown American named Van Cliburn walked away with first prize in piano, the Tchaikovsky Competition is held every four years at the Moscow Conservatory and Tchaikovsky Concert Hall. This year's competition, the 10th, promises once again to be a feast for music lovers and an unparalleled opportunity to discover musical stars of the future.

The major prizes of the competition are awarded in four categories -- piano, violin, cello and voice. Participants are gradually eliminated through three rounds of playing and singing, as panels of distinguished judges choose the six prize winners in each instrumental category and the four prizes in voice. Occasionally, the judges decide that none of the contestants is worthy of a first prize. More often, a single prize is shared by two musicians considered of equal merit.

Prizes will be announced and awarded at a ceremony on July 1. The following evening, first-prize winners will play and sing the music of Pyotr Ilyich Tchaikovsky at what is probably Moscow's musical event of the year, the Competition's Gala Concert.

For many, though by no means all, past winners, the Tchaikovsky Competition has acted as a springboard to international acclaim. Those who have taken first prize include pianists Vladimir Ashkenazy, Andrei Gavrilov, and Mikhail Pletnyov, violinists Viktor Tretyakov, Gidon Kremer and Viktoria Mullova, cellist Nathaniel Rosen, and singers Vladimir Atlantov, Yelena Obraztsova and Yevgeny Nesterenko. A recent Moscow concert uniting winners of the 1970 Competition left little doubt that at least two of them, violinist Kremer and cellist David Geringas, can be counted among the finest exponents of their respective instruments.

Although foreigners have always been included in the panels of Tchaikovsky competition judges, past competitions often displayed more than a little bias toward Soviet musicians. Whether the same will be true under the vastly changed circumstances of Russia in 1994 remains to be seen.

A preliminary contest among stringed-instrument makers initiated the competition on May 28 and will conclude on Wednesday. The main events begin Friday when the piano contestants start their first round of play. From then until the final day of competition on June 30, music lovers will have an opportunity to hear morning, afternoon and evening performances every day except June 25.

The schedule of events is as follows:

Piano: June 10 to 18 at 1 P.M. and 6 P.M; June 20 to 24 at 10 A.M. and 6:30 P.M.; and June 26 to 29 at 7 P.M. All events in the Conservatory Great Hall.

Violin: June 13 to 17 at 10 A.M. and 6 P.M. in the Tchaikovsky Concert Hall. June 19 at 11 A.M. and 6 P.M.; June 20 to 24 at 2:30 P.M.; and June 26 to 29 at 3 P.M. in the Conservatory Great Hall.

Cello: June 14 to 18 at 11 A.M. and 7 P.M. and June 20 to 24 at 11 A.M. and 6 P.M. in the Conservatory Small Hall. June 26 to 29 at 7:30 P.M. in the Tchaikovsky Concert Hall.

Voice: June 20 to 24 at 5 P.M.; June 26 to 28 at 1 P.M. and 4 P.M.; and June 30 at 7 P.M. all in the Tchaikovsky Concert Hall.

Winners will be announced at 6 P.M. on July 1, followed by the Gala Concert at 7:30 P.M. on July 2, both in the Conservatory Great Hall. Tickets to all sessions can be obtained at the Conservatory (13 Ulitsa Gertsena, metro Arbatskaya) and the Tchaikovsky Concert Hall (4/31 Triumfalnaya Ploshchad, metro Mayakovskaya), depending on the concert location, as well as through IPS Theater Box Office at the Hotel Metropol (telephone 927-6382).