Elena Mukhina, the sensitive Soviet gymnast who won the women's all-around world championship in 1978 and dreamed of regaining her lost form at the Moscow Olympics, crushed several vertebrae in her neck in a training accident and is hospitalized in Minsk following surgery, Soviet officials reported today.

The tiny, 20-year-old gymnast, whose erratic performances were blamed by coaches on her poetic and romantic nature, reportedly landed on her neck while practicing difficult acrobatic routines by herself. She was taken unconscious to a hospital.

Her condition was unclear. Some reports said doctors feared she was paralyzed, while others said she has use of her arms and legs and is able to speak. She has been placed in a neck cast and will be immobilized for several weeks.

According to the reports Mukhina was practicing the difficult maneuvers in disregard of orders from her coach and virtual foster father, Victor Klimenko, who had left Minsk for Moscow. He returned immediately when informed of the accident.

Mukhina took up gymnastics late, at age 9, but won the Soviet junior championship within six years. Two years ago, at 17, she captured the world spotlight by defeating Romanian Nadia Comaneci, the heroine of the 1976 Olympics, for the world title in Strasburg.

In last summer's Spartakiad, the Soviet Union's sports festival that was opened to other nations as a dry run for the Olympics, Mukhina was the favorite, but finished 14th among her countrywomen and was criticized in the press for her "frivolous" approach to training.

"She is too easily touched," a team coach said at the time. "She is too sensitive. She likes music, poetry and to sit and think. She is too sensitive a girl to be a great athlete."

Asked her hobbies at a press conference, Mukhina said, "I read books . . . I like Ernest Hemingway most of all. The Old Man and the Sea."

Her disappointing performances continued after the Spartakiad, and her attempts to live up to the promise of 1978 were hampered by a series of injuries last year that had demoralized her. She was relegated to alternate status on the strong Soviet team for the Olympics, but still hoped to regain her place on the team and captivate the home fans.

Now she will watch the games from her hospital bed, her future uncertain but her gymnastics career surely ended. The Moscow Games have not even begun, but this must be one of their saddest stories.

Moscow remained quiet today, devoid of the festive atmosphere that usually envelops the host city a week before the Olympics. Only about 1,600 of the 5,000 athletes expected -- half the total that was anticpated before the U.S.-led boycott of the Games because of the Soviet invasion of Afghanistan -- have moved into the Olympic Village.

A delegation of boxers and wrestlers from Afghanistan moved into the village Saturday. Afghan officials would not confirm reports that seven wrestlers had defected last week to Pakistan rather than come to Moscow.

The Afghan athletes here talked to Western reporters, but sidestepped all political questions.

Tatyana Biryulina, 24, a Tashkent student who had not expected to qualify for the Soviet team, set a world record in the javelin in the final trials at Podoysk, about 50 miles from Moscow.

Biryulina became the first woman to throw the javelin more than 70 meters. Her throw of 70.08 meters eclipsed by 12 centimeters the world record set by East German Ruth Fuchs at Split, Ugoslavia, this spring.