Bonnie Moore, an 18-year-old dancer from the Washington Ballet, won a bronze medal yesterday at the prestigious International Ballet Competition at Varna, Bulgaria. It was also reported unofficially that Choo San Goh, assistant artistic director of the Washington Ballet, will receive a choreography award.

Moore and her Washington Ballet partner, John Goding, performed a pas de deux from Goh's 1979 ballet "Momentum" during the competition's final round.

Moore won a first prize in Switzerland's Prix de Lausanne ballet competition last year, and first prize in this country's National Society of Arts and Letters ballet competition in 1980.

Reached by telephone in Varna yesterday, Moore said, "I think I danced as well as I could have under the circumstances." The competition has been in progress since July 8, and rehearsals have been held in early morning hours. Moore said some nights she didn't get on stage until 3:30 in the morning.

"This was a very different experience from other competitions I've been in," she said. "There were many more contestants, and the dancers were all of very high caliber."

Moore was born in Phoenix and had her early ballet training at the Arizona Academy of Dance in Tempe. In 1980 she came to the Washington Ballet as a student; this past year has been her first season as a full company member.

Moore's award is also another feather in the well-studded cap of Mary Day, artistic director of the Washington Ballet. Since 1972, Day has entered Washington Ballet dancers four times in international competition and come away with prizes each time, including, in 1981, the gold medal that Amanda McKerrow became the first American ever to win in Moscow.

The world's oldest such event, the Varna ballet competition has been held 11 times since 1964. Among previous winners have been Mikhail Baryshnikov, Natalia Makarova and Fernando Bujones.

Moore and Goding were scheduled to perform in Varna again last night during a gala award celebration.