Through their churches, American kids are sending a colorful stream of good wishes to their counterparts in the Soviet Union as the 1,000th anniversary of Christianity there is noted.

"I love you," many of the youngsters scrawl on their hand-fashioned cards, decorated with brightly hued figures. "Let's be friends . . . write to me."Called a child-to-child "crayon brigade," about 40,000 cards have been received by the National Council of Churches for relay to children of Soviet church members.

The cards are being carried personally in batches by church groups visiting Soviet churches this year. Groups went in April and May and others go in this month, as well as in August, September and October.

Many Protestant, Roman Catholic and Eastern Orthodox leaders from this country and elsewhere visited the Soviet Union for special celebrations June 5-16.

But it is the outpouring of fond, joyful artwork by children in more than 3,000 Sunday school classes in about 60 denominations that provided the sentimental touch.

"It was an overflowing of children's naturalness," says Suzanne Nagel, a New York Episcopalian who originated the project, asking churches across the country to send cards made by youngsters.

She says some include photos of themselves and families, and adds, "These are really meaningful. They're personalized, so the receiving Soviet child can say, `See, my American friend has brown hair.' "

Many of the cards, which have come from children in all 50 states, are decorated with crosses, hearts, flags, birthday cakes, balloons, trees, flowers and smiling faces.

Besides wishing "happy birthday," many cards include expressions of affection and cheering hopes.

There also are typical childish misspellings, such as "Habbi 1000" and "prays the Lord."

"We want to be friends with our brothers and sisters in Christ in the USSR, and we send these handmade birthday cards as tokens of friendship," wrote the teacher of a Denver Sunday school class.

When some of the cards were being distributed to Soviet children at a church in Kiev, "mothers had tears in their eyes," says the Rev. John Lindner, who led a U.S. tour group there in April.