It was a scene that might have never happened, at least not without bloodshed, in 10-year-old Robbie McLaughlin's hometown of Belfast, where Catholic and Protestant live separated by concrete walls and barbed wire.

But there he was yesterday, a Catholic, seated side by side with Protestant children in a Catholic Church in Silver Spring, listening to sermon by an Episcopal minister.

Robbie is one of 23 Irish children, Protestant and Catholic, who have spent the past six weeks living with families from the Washington area as part of the privately sponsored Belfast Children's Summer Program. The aim is to give children, ages 9 to 11, a brief hiatus from that city's segregated neighborhoods and its daily diet of tension and street violence.

The American families who take in the children are told not to talk with them about the political and religious strife in Northern Ireland or lavish them with gifts. They are asked to try to give them as normal a slice of American life as can be found in the American suburbs.

Blue-eyed, black-haired Seamus Millan got his first taste of Little League baseball and wants to take a baseball bat back home with him so he can start his own team.

Robbie McLaughlin, a hazel-eyed, dimple-faced boy, has been to see "Return of the Jedi" and Fourth of July fireworks on the Mall, has spent Saturdays wandering around shopping malls. He also took swimming lessons at a public pool.

Ten-year-old Catherine Gallagher, who has won awards back home for her Irish jig, lived with a family from Mount Rainier that has adopted an American Indian girl and a South American boy. She played every day with the black and white children who live on the block.

In between were a lot of other lessons for Catherine and the other children, who told of street riots, seeing soldiers at rifle practice and being frisked before they could enter stores back home.

"Recounted Dave Shannon, whose family Robbie is staying with in Silver Spring: "One night we were just sitting out on the back porch and Robbie said, really out of nowhere, 'It's so peaceful here.' It really brings home to you that what you read about what's happening in Belfast, the violence you see on TV, is happening in this boy's life."

The first time Robbie saw the Shannons' back yard, which sits on a three-quarter-acre lot and faces a wooded area and a creek, he asked incredulously, "Is all this yours?" Then, they said, he ran around and around the yard until he tired himself out. Shannon, personnel director for the Federal Reserve Board, said the first time Robbie went to the pool, "He was very surprised to see that Protestants and Catholics use the same pool with no recrimination or antagonism."

Bernard Vincent, whose family Catherine Gallagher is staying with in Mount Rainier, said Catherine was frightened at first about sharing a room with his daughter Dana, an American Indian. "I think it was all this stuff they've seen and heard about the Indians," said Vincent, a drafting engineer.

But now the two girls are inseparable, he said. They do the dishes together and have taken trips to New York and Philadelphia with Dana's majorette team, the Mount Rainier Eaglettes.

"The first day all Catherine did was cry. But she hasn't been homesick yet. In fact, I've had to urge her to write her parents over the six weeks."

Yesterday, in their final full get-together before returning to Ireland next Thursday, the children sat up on the altar of St. John the Baptist Church on New Hampshire Avenue. There, the Rev. Earl Mullin of St. John's Episcopal Church in Georgetown told them to imagine that a plain white cloth was hanging from the ceiling to the floor.

"Now I want you to weave many different colors into that cloth . . . so that in this cloth there are lots of different elements . . . . Now if someone says to you, 'You're different, I don't want you around,' do you know what happens to that fabric? It becomes torn."

There are also some important lessons, too, for the American children, according to their parents. They begin to see things they take for granted, such as movies, showers and telephones, through the eyes of children who consider them novelties, the parents said.

"Whole neighborhoods come around and respond to these children," said Thomas Craven, a clinical psychologist from Wheaton who is one of the organizers of the program. "And for Washington, to see whole neighborhoods do anything is amazing."

Funds for the program are raised privately through churches, businesses and fraternal organizations. It costs about $500 to bring each child to the states. The host families provide the necessities while the children are here.

Most of the families hear about the program through local churches. The families are interviewed and carefully screened before they are selected, said the program's chairman, Ray Walsh, a systems analyst for IBM.

This is the second year the program has been in Washington. Last year, only five children came. This year, the program was much expanded and included receptions at the English and Irish embassies for the children and their families and a service at the Washington Cathedral.

When the Irish children return again to Belfast, and the hostility between Catholics and Protestants, they may only be able to acknowlege each other with a nod, said Walsh. "But at least once in their lives," he added, "They will have had exposure to a situation where it's not that way."