Even though bigger and more statuesque than four years ago, Nadia Comaneci will never be confused with Bo Derek -- but she's still a "10" on the balance beam.

The Exquisite Romanian gymnast, who captivated the 1976 Olympics in Montreal as a pigtailed 14-year-old who never made a mistake, picked up where she left off four years ago as the absorbing battle for supremacy in women's gymanastics began today at the Moscow Olympics.

In physique, Comaneci bears little resemblance to the tiny, tight-lipped sprite who made the Montreal Games a personal tour de force. She is bigger, fuller, more muscular. The pigtails are gone. She is a woman instead of a little girl.

But maturity does not seem to have had any negative effect on her skills, as it did on Olga Korbut -- the gymnastics star of 1972 who flopped in '76.

Comaneci, fully recovered from the infected hand that forced her to drop out of the world championships in Fort Worth, Tex., last December, earned a row of perfect scores in today's compulsory exercises.

However, the gifted and determined Natalya Shaposhnikova -- the Soviet star who won last year's Spartikiad here and is described by her admiring coach as being "prickly like a hedgehog" -- matched Comaneci 10 to 10 in her best event, the vault.

Shaposhnikova and Comaneci posted identical marks of 9.95 in the three events in which they were not perfect. After the day's remarkable compulsories in balance beam, vault, uneven parallel bars and floor exercises, they were tied.

"Such high marks are unheard of in international competition," said a Soviet gymanastics expert after watching the brillant activities at the Luzhniki Sport Complex. "It has happened in national meets but never at the Olympics or World Championships."

East Germany's Maxi Gnauck, reigning world champion in the uneven bars, scored 9.95 on two apparatus and 9.90 on the others for a total of 39.70 and third place in the intermediate standings. These count toward both the team competition and qualification for the all-around and individual apparatus titles scheduled later in the week.

Nelli Kim, the dynamic Soviet who won the all-around gold medal in Fort Worth, scored four marks of 9.90 and is in fourth place.

The astonishingly deep Soviet team -- which desperately wants to reclaim the supremacy it relinquished to Romania in Fort Worth, even with Comaneci sidelined -- led the team standings, to the delight of 10,000 spectators.

The Soviets have 197.75 points to 196.80 for East Germany and 196.70 Romania.

Comaneci now weighs 99 pounds and wears her hair in a pageboy coiffure. She graduated from high school last month. Times have changed, but she displayed the same grimly serious expression and total concentration that became intimately familiar to millions who watched the Montreal Olympics on television.

She is favored to win the all-around title, but Shaposhnikova, Gnauck and Kim should make it a magnificent competition -- one of the most memorable of these Olympics that have been boycotted by the United States, Canada, Japan, West Germany, China and about 45 other nations because of the Soviet invasion of Afghanistan.

The Communist bloc nations continued to pile up gold medals and world records today, but their monopoly was broken by 18-year-old Swedish engineering student Bengt Baron. He unexpectedly won the 100-meter men's backstroke and was so thrilled he leapt from the pool at the Olympic swimming complex like a dolphin.

Barbara Krause won the women's 100-meter freestyle, breaking the Olympic and world record she had set in a preliminary heat 24 hours earlier and leading East Germany to a sweep of the medals in the event.

That was no surprise. In the absence of the American women swimmers, East Germany against the rest of the field was a little like Jaws versus a 90-pound weakling swimming with cramps and a bloody nose. Not much of a contest.

Krause, 21, a hefty police sergeant, took the gold medal with a time of 54.79. Monday she swam her qualifying heat in 54.98, breaking her own 1978 world record of 55.41, the first woman to better 55 seconds. "Yesterday I broke a world record, today I improved it again, but now I'm the Olympic champion, that is much more important to me," she said.

Teammate Caren Matschuck was second in 55.16, and Ines Diers was third in 55.65. Krause expressed disappointment at not being able to compete against the Americans, who were swamped by East Germany in Montreal but recoverd in the 1978 World Championships at Berlin.

"They trained hard and were well-prepared," she said of the Americans. "Still, after tonight's world record, I consider myself the fastest freestyler in the world."

East German Ines Geissler beat her countrywoman Sybille Schonrock by one-hundreth of a second to win the gold in the women's 200-meter butterfly. Geissler's time of 2:10.44 set an Olympic record, but was far off the world record of 2:07.44 set last year by American Mary Meagher.

Sergei Kopliakov of the Soviet Union won the gold in the men's 200-meter freestyle. His clocking of 1:49.81 erased the Olympic record set by American Bruce Furniss in 1976, but was short of American Rowdy Gaines' world mark of 1:49.16, posted this year.

Kopliakov, who was encouraged by deafening shouts, applause and rhythmic stomping as he accelerated to victory over the 25 meters, is the second Soviet man to win a gold medal in swimming here. Sergei Fesenko became the first in the 200-meter butterfly Sunday night.

Another Soviet, Viktor Kunznetsov, was favored to win the 100-meter backstroke, but Baron foiled him -- to the grand delight of his fellow Swedes -- and became the first athlete from a non-Communist bloc country to win a gold medal here.

Kunetsov was listed in the program as having finished third in the 1978 World Championships. The Soviet hosts neglected to footnote that result to indicate that he was later disqualified for failing the dope test.

Nonetheless, Kuznetsov was clearly confident. When the other swimmers stepped forward and nodded or raised a hand to acknowledge applause. Kuznetsov danced foward, bowed flamboyantly from the waist, raised both hands high over his head, and waved an extended arm in all directions.

He swam a good race, But Baron outdueled him the final 50 meters and won 56.53, compared to American John Naber's 55.49 Olympic and world record of 1976. Kuznetsov was second in 56.99.

At the end, Baron ripped off his swimming cap in the gold and blue Swedish colors and jumped high from the water in an exultant leap that Flipper would have loved.

The few Swedes in the stands whooped it up, and Swedish journalists and photographers ran to mob their new hero. On the victory stand, the boyishly handsome Baron pumped his arms triumphantly as he received his medal, again when his name was announced and a third time after the Swedish anthem was played.

"I never dreamed or thought I could do this," he said later. "I still can't understand that I won the Olympic gold medal. This is my first big championship. I never swam in European or World championships before. I thought Kuznetsov would win."

So did Kuznetsov. But after all, the Communists, who also picked up golds today in diving, weightlifting and shooting, can't win all the medals, even in a boycotted Games.