Bonnie Moore, the 18-year-old Washington Ballet dancer who won a first prize in Switzerland's Prix de Lausanne competition a year ago, will be entered this July in the prestigious international ballet competition at Varna, Bulgaria.

Mary Day, artistic director of the Washington Ballet, who made the announcement yesterday, will accompany Moore to the contest. Dancer John Goding will partner Moore in the three-round event, which takes place July 9 through 24. The Varna competition, the oldest of its kind, is held every two years.

Moore, born in Phoenix, started her dance studies at the Arizona Academy of Dance. She came to the Washington Ballet as a student in 1980, and that same year won first prize in the National Society for Arts and Letters nationwide ballet competition. She now is completing her second season with the Washington Ballet as a full company member.

Commenting on the decision to enter Moore at Varna, Day said yesterday: "I only think in the direction of a major international competition when I find someone whom I consider to have exceptional ability. Bonnie is very gifted and I feel confident that she will be well received at the Varna competition."

Since 1972, Day has entered four prote'ge's from the Washington Ballet in international contests, and each has returned with a prize. Besides Moore's award at Lausanne, Amanda McKerrow (now with American Ballet Theatre) became the first American to win a gold medal in Moscow in 1981; and at Varna in 1972, Kevin McKenzie (now a principal with ABT), won a silver medal, while Suzanne Longley (currently a principal with the Houston Ballet), won a bronze.

Moore's contest repertory at Varna will include the pas de deux for Odette and Siegfried from Act II of "Swan Lake" and a pas de deux by Choo San Goh, the Washington Ballet's assistant artistic director. Moore, Goding and Day will depart for Varna on July 6.