The Bolshoi Ballet returned here today to a subdued welcome after a North American tour marked by three dancers' defections that have brought unprecedented political embarrassment to the Soviet Union's proudest and most renowned artistic company.

As they filed slowly through customs formalities into the waiting arms of bouquet-toting family and friends at Sheremetyevo airport, the 135 dancers, choreographers and masseurs seemed still stunned by the defections of dancers Leonid and Valentina Kozlov, who slipped away during the confusion of the troupe's final American curtain call in Los Angeles Sunday night.

A young dancer recounted the company's "utter surprise" to be told by Soviet officials on the way to the airport departure Monday morning that the Kozlovs were absent from the bus because they had defected to the United States. "We thought they had simply overslept," she said, adding that she had "no explanation" to offer about their action.

The young woman, a member of the corps de ballet who asked to remain anonymous, said the company "was very nervous" during most of the tour because of the Aug. 22 defection of Alexander Godunov, a principal dancer, shortly after the Bolshoi arrived in the United States.

Godunov's defection touched off a bizarre, three-day Soviet-American confrontation when U.S. officials refused to allow a Soviet jetliner to leave New York's Kennedy airport until they were sure his wife, Ludmila Vlasova, wanted to return to the Soviet Union and not join him in the United States.

Vlasova's return received maximum coverage by the Soviet media, which turned out in force with television crews and cameras to welcome her, and denounce U.S. "special services" for enticing her hus- band to defect with "mountains of gold and rivers of liquor."

In sharp contrast to the treatment accorded Vlasova's return, the company's arrival here went unrecorded by the media, and the Soviets so far have had nothing to say about the defection of the Kozlovs.

However, Vyacheslav Sordeyev, a leading young dancer whose wife, Nadezhda Paviova, is a prominent young Bolshoi star, remarked as he left the arrival hall that "nobody regrets that Kozlov left, because nobody liked him. It was very unexpected, and nobody can understand why they did it because they have always gotten good parts in the troupe." He said there are many "good young dancers to substitute, so it's not a big loss."

But reliable sources in Moscow's dance community report that the defections may in fact reflect a fierce internal battle over the Bolshoi's artistic direction, which centers on artistic director Yuri Grigorovich. He accompanied the troupe to America and unwittingly increased its embarrassment by choosing future defector Ko,lov to succeed defector Godunov in several main roles.

These sources say Grigorovich, who was whisked by official car directly from the plane today and thus avoided any encounters with Western correspondents, is a stiff ideologue whose unyielding artistic conservatism has sparked deep resentments and bitterness within the company. Over the years, Western dance critics who have seen the Bolshoi on its frequent tours outside the Soviet Union, have found its productions technically accomplished, but lacking in bright new ideas that lie at the heart of artistic panache.

The Moscow sources say the Bolshoi, which numbers 270 dancers, has split roughly into three groups which are at odds with each other. The artistic conservatives are said to cluster around Grigorovich, while the "liberals" have taken prima ballerina Maya Plisetskaya as their champion in seeking artistic innovations that can keep the company in the forefront of the world's ballet groups.

A third group, said to be moderates seeking a compromise between the two extremist camps, look to dancer Vladimir Vasilyev, a stirring performer who now is achieving distinction as a choreographer.

So deep is the tension, says one source, that Plisetskaya, 53, has refused to dance in any of Grigorovich's major productions.

How much of all this is volatile artistic temperaments at work on each other, and hou much is genuine creative disagreement is virtually impossible to say. But in the Soviet system, where political ideology has always played a heavy-handed role in determining the limits of artistic freedom, such matters take on a significance unknown in the West.

Indeed, the defections over the years of such luminous talents as Mikhail Baryshnikov, Rudolph Nureyev, and Natalia Makarova-- all from the artistically more adventuresome Kirov Ballet of Leningrad-- have centered on the artists' needs for the greater artistic freedoms they believe they could find in the West. Each one of these earlier defections has brought considerable political embarrassment to the Soviets, who like to present an image of the world's most artistically creative society.

The fact that the three defections occurred while Grigorovich was leading this troupe-- the first such political defections in the Bolshoi's 203-year history-- seems certain to exacerbate artistic-ideological tension within the company.

The Moscow artistic world-- as well as many Western observers-- will be watching the Bolshoi in coming months for signs of the effects of the defections.

One dancer underscored the uncertainty today: "We haven't had any meetings yet to see where this takes us," he said.