Renata Babak had dialed the international operator every 15 minutes, it seemed, since Monday, when the news of a Soviet nuclear power plant explosion left her fearing that her parents in Kiev might be dead. "Later, later," Babak said the operators kept telling her, until yesterday, when they put through a call and the faraway voice of her 70-year-old mother came on the line.

"First my mother was very excited I called," said Babak, a former Bolshoi Opera star who defected in 1973 and now lives in Washington. "I asked how do you feel and she did not understand why . . . . They don't know. They not realize. On radio, they listen. But they hear there's nothing to worry about because two people died."

Babak, who grew up in Kiev, said her mother had heard on the radio that there had been an accident but that there "was no danger, no radiation, you can drink the water, everything is okay . . . . When I say, 'Mother, do not drink the water, go from Kiev,' she was very astonished."

Babak said her mother told her that she and Babak's father, who is 75, were suffering from respiratory problems, a flame-like feeling in their throat and dizziness -- symptoms, Babak fears, of radiation.

Babak is one of a handful of Ukrainians in the United States who have reached relatives in the Soviet Union since the disastrous explosion at the Chernobyl nuclear plant about 60 miles from Kiev.

About 40 members of the Ukrainian community in Washington, many of whom are waiting for word about their own loved ones, held a candlelight vigil last night near the Soviet Embassy on 16th Street to commemorate victims of the nuclear accident. According to the Soviets, the accident has killed two persons and hospitalized 148.

"The community is urging the Soviets to allow technical and humanitarian assistance, to lift restrictions on parcels . . . to let the media in so that the damages can be accurately reported to alleviate distress among people who are very concerned . . . ," said the Rev. Joseph Denischuk, of the Ukrainian Catholic National Shrine in Northeast Washington.

The Ukrainian community in the Washington area is small, about 5,000 to 7,000, according to a spokesman, and many in Denischuk's parish have only recently come to the United States and fear retaliation for their families back home. The Ukrainians' homeland is one of 15 republics in the Soviet Union.

"Every family is afraid," said Denischuk. "They have relations in the Ukraine . That is why they don't really want to talk."

But Nadia O'Shea, a former State Department employe who is of Ukrainian ancestry but has no close relatives in the Soviet Union now, was bolder. "This is all quite typical of the Russians," she said. "The Ukrainians are always striving for freedom, so they think if a few thousand die, so much the better."

Babak, who defected when the Bolshoi Opera was at La Scala in Milan, also has been an outspoken critic. The Soviets "have not done anything . . . , " she said yesterday. "People will perish because they have not accepted the proposal of American help."

As to the atmosphere in Kiev, she said her mother told her that people "feel there is something wrong . . . . But they are afraid to talk one to another. People are scared."

Babak said her mother began to cry before ending their conversation with the words, "I want before I die to see you."

But Babak said she held back her tears. "There is no time to cry, and now I am so angry . . . angry at the government, that they so cynically do not say there is danger. That's what I'm angry at. That this happened."