The Rev. Benjamin Weir, a former missionary to Lebanon held hostage there for 16 months, was elected Wednesday to lead the Presbyterian Church (U.S.A.).

"I am aware that we live in a complex world and my church is realizing that in my election," Weir said after his election as moderator of the denomination of 3.1 million people, formed when the Northern and Southern branches of the Presbyterians merged in 1983.

Weir, 62, defeated two other candidates, winning on the first ballot with 356 votes. He needed 323 to be selected the new leader, or moderator, by the more than 600 delegates to the 198th General Assembly of the Presbyterian Church (U.S.A.).

At a news conference and in a speech to delegates before the vote, Weir referred often to his experience as a captive of Shiite Moslems in Lebanon and to the efforts of the church and his family in pressing for his release. He urged the church to remember the Americans still being held captive in Lebanon.

Americans still missing or being held there are Terry Anderson, 38, chief Middle East correspondent for The Associated Press; William Buckley, 58, a political officer at the U.S. Embassy in Beirut; the Rev. Lawrence Martin Jenco, 51, a Roman Catholic priest from Joliet, Ill.; David Jacobsen, 54, administrator of American University Hospital, and Thomas Sutherland, 55, acting dean of agriculture at the American University of Beirut.

Weir was born in Salt Lake City, and has been on home assignment in the United States since his release in Lebanon. At the time he was abducted, he was a Christian education consultant to the National Evangelical Synod of Syria and Lebanon. He had served in Lebanon since 1953 in various capacities, including relief work.

Since his release, he has been visiting congregations, presbyteries, synods and institutions throughout the church speaking about his Middle East experiences. He also has spent some time writing.

Prior to going to Lebanon he served as an assistant pastor in Oakland, Calif., and was a chaplain in the U.S. Army during the Korean War. He received his bachelor of divinity degree from Princeton Theological Seminary.

Weir's election ended an effort by the Rev. Paul Moon, a native of Korea, to become the first Asian American to become leader of U.S. Presbyterianism. Moon, who is pastor of Bethany Presbyterian Church in Huntington Station, N.Y., was second with 183 votes.

The third candidate, the Rev. Carroll Shuster, pastor of the First Presbyterian Church of Coral Gables, Fla., had 105 votes.

Weir succeeds William Wilson as moderator, the highest elected office in the church. The moderator, who serves a one-year term, presides over the general assembly, travels widely and makes committee appointments.

Weir said he will spend the year visiting churches and interpreting to the church actions taken by the General Assembly. He also said he and his wife, Carol, are working on a book tentatively titled, "Hostage Bound, Hostage Free." They expect it to be available next spring.

A design for the structure of the new church and a site for a new headquarters are expected to be major topics at the General Assembly, which began Tuesday and will end Wednesday.