Equally divided between Muslims and Christians, 16 teen-agers from war-torn Beirut have arrived in the United States to spend the summer in a more peaceful atmosphere. They were brought to the United States over the weekend by the Fresno-based Children's Committee, which places Protestant and Catholic children from Northern Ireland with U.S. families each summer. The Northern Ireland program is providing vacations for 204 youngsters this year. Vincent Lavery of Fresno, who has spearheaded the trips from Northern Ireland, organized a committee of Muslims and Christians in Beirut this spring to plan the trip. The committee met several times, despite personal risks, Lavery said. One Muslim youth and one Christian were paired to stay with the same host family for six weeks.