CHICAGO (AP) _ A small congregation of Ukrainian Baptists today awaited the arrival of 20 new members from the Soviet Union, all from one family who for years were harassed because of their religious beliefs, a minister says.

Vladimir Khailo, 55, his wife Maria, 50, 10 of their 14 children, five grandchildren and three in-laws were scheduled to arrive tonight at Chicago's O'Hare International Airport.

Awaiting them will be an 11-room apartment, paid for by the Ukrainian Baptist Church in suburban Berwyn.

The Rev. Olexa Harbuziuk, pastor of the church, said Khailo, of the small industrial town of Krasny Lootch, spent six years in a mental institution because of his belief in Christianity and his evangelism.

''We learned about his plight in 1980 and started writing all kinds of letters and talking to various people to get him released,'' said Harbuziuk. ''And we started praying for his release.''

The congregation's letter-writing campaign and efforts by Christian Solidarity International, an organization dedicated to religious freedom that is located outside Washington, D.C., helped gain the release of Khailo and most of his family.

''I feel that this (family's release) is a great thing,'' Harbuziuk said. ''This is the end of their oppression and the beginning of freedom for them.''

Steve Snyder of Christian Solidarity said two of Khailo sons are still held in a Soviet mental institution. A third son is serving in the Soviet Army.

For three months, members of the family have been gathering in the Netherlands for the journey to the United States.

''We will take care of the entire family,'' Harbuziuk said. ''We don't have employment for them now, but several companies have promised jobs.''