Two members of a Siberian Pentecostal group permitted to leave the Soviet Union after a 23-year struggle said yesterday in the Capitol that they never lost hope during their ordeal--even when seven of the dissidents were isolated for five years in tiny basement quarters at the U.S. Embassy in Moscow.

Liuba Vashchenko, 30, said her 16-member family was given no reason by the Soviets for finally being allowed to emigrate.

"It is difficult to understand the Soviet government or why they do things," she said in the group's first U.S. press conference. She spoke in English softly and without emotion. "I think all problems have an end, and this one just ended."

Appearing with her sister Nadya, 29, and Sens. Carl Levin (D-Mich.) and David L. Boren (D-Okla.), Vashchenko thanked the many Americans who have worked for her family's release and said she and her relatives hoped to settle in Israel, where most of the family has stayed since leaving the Soviet Union two weeks ago.

Levin, who spearheaded a drive to help free the Protestant fundamentalists, said another family of 15 Soviet Pentecostals arrived yesterday in Vienna, on their way to Israel, where they would join the Vashchenkos.

U.S. State Department officials have linked the families' release to an East-West conference on security and human rights nearing a conclusion in Madrid.

The Vashchenko sisters, who were brought here last Wednesday by a Christian human rights group named Friends of the West, will remain in the United States "for three years or more to attend colleges and university," said Liuba Vashchenko.

After reading a prepared statement, she said she planned to study law in addition to Hebrew and English. Nadya Vashchenko, who does not speak English, will concentrate on languages, Liuba said.

Asked for her impressions of the United States, Liuba said she has "seen only a little bit. I cannot make a general opinion, but I like this country."

Smiling shyly as reporters edged forward to hear her comments, she explained that she hoped to study law in California.

"I was not there yet," she said, "but I think I will like it."

Liuba Vashchenko, who wore a simple brown skirt and white blouse, described the five years she and six other people, four of them her relatives, lived in the basement of the U.S. Embassy in Moscow.

"I was very busy," she said, "writing letters to people, making phone calls, learning English, a little French. My mother and some of the women were all the time knitting things for friends and for children."

The seven refugees lived in two cramped basement rooms after they had rushed past Soviet policemen on June 27, 1978, to get into the embassy.

"We were able to cook and to live," said Liuba Vashchenko. "There was not so much difference from what we had before during those five years."

Dubbed the "Siberian Seven" during their long protest against Soviet restrictions of religious freedom, the Pentecostals left the embassy in April, after another Vashchenko sister, Lidia, was given permission to emigrate.

Pyotr Vashchenko, 55, patriarch of the family, first applied to emigrate from the family's hometown of Chernogorsk, Siberia, in 1960.

Liuba Vashchenko said yesterday that the family wanted to live in Israel "to be free there."

She added that "there are many, many others" of her faith in the Soviet Union who want to leave.

Levin said he had spoken by telephone yesterday to members of the 15-person Chmykhalov family, which had arrived only hours earlier in Vienna.

Timofei Chmykhalov, 21, who with his 60-year-old mother Maria had joined the Vashchenkos in the U.S. Embassy, said leaving the Soviet Union "was like a dream come true," said Levin.

Liuba Vashchenko said she also had spoken with several of the Chmykhalovs yesterday. "They sound fine, but tired," she said. "And I can understand that."