The Rev. Dr. Arthur McKay of Cincinnati first stepped into the pulpit of the historic New York Avenue Presbyterian Church yesterday as the guest preacher. He returned to the sanctuary less than two hours later as the congregation's unanimous choice to succeed the Rev. Dr. George Docherty, who retired as senior minister last August.

The selection of Dr. McKay, who is nationally known as an outstanding churchman and theological educator, culminated a 16-month search, by the congregation's Vacancy Committee.

Dr. McKay emerged the winner over 253 other candidates for the $31,835-a-year post. Ralph Reeder, chairman of the Vacancy Committee, said the total candidate list included 10 women and at least five members of racial minorities.

Presbyterians hire and fire their own ministers, unlike Roman Catholics or Methodists who clergy appointments are made by a bishop. Technically, the "call" issued yesterday to Dr. McKay by the New York Avenue congregation does not become final until it is approved by the local presbytery, the regional association of Presbyterian churches.

Presbytery approved is required to assure that doctrinal and other standards are maintained in local congregations. In practice, a presbytery will not override the wishes of a congregation without grave reason; Dr. McKay's endorsement by the local National Capital Union Presbytery can be assumed.

Dr. McKay, currently senior pastor of Knox Presbyterian Church in Cincinnati, was president of McCormick Theological Seminary in Chicago, a major Presbyterian seminary, from 1957 to 1970. From 1970 to 1973 he was president of the Rochester (N.Y.) Center for Theological Studies, an ecumenical clustering of Baptist, Episcopal, Roman Catholic and interdenominational seminaries. The author of several books, he has preached lectured widely.

The search for new pastor at the 173-year-old New York Avenue Church, where Abraham Lincoln and a half-dozen other Presidents worshipped, began with a survey of church members to determine the qualities they felt a senior minister should have, Reeder said.

"Preaching, pastoral concern, counseling, interest in the downtown urban church, ecumenical attitude and understanding and what that means for this church in this city, openness to new ideas, management and administrative ability. Christian education . . ." were qualifications the committee sought, Reeder said.

Preaching, a central function in all Protestant churches, is especially important at New York Avenue Church, whose 1,232 largely white, largely middle-class members are dispersed throughout the surrounding suburban area.

"Preaching," said Reeder, "is what pulls people to the downtown area, "bringing them past other churches of their denomination along the way. Without a compelling preacher, church sociologists say, churches like New York Avenue are doomed.

Although the Vacancy Committee earlier has sent copies of Dr. McKay's impressive credentials, along with the committee's unanimous endorsment of him, to all members of the church, it was his preaching yesterday that appeared to clinch his election.

Preaching "On garden-variety sainthood" Dr. McKay observed that "the wonderful thing about saints is that they were human: they got hungry, they lost their tempers, they scolded Gold . . . but still they went on, blundering their way toward him (God)."

St. Paul's admonitions to the saintly life, he continued, were directed at "garden variety Christians, frail men and women just like ourselves . . . constantly slipping from the heights of Christian conduct "but nevertheless "called to be God's men and women."

To be a saint, he summed up "is to believe in God and to be a disciple of Christ."

At the close of the service, the white-haired preacher and his wife, Ann, stood near the front of the handsome white, blue and gold sanctuary, greeting a long line of worshippers.

Fifteen minutes later, the business meeting was called to order. While Dr. McKay waited outside, Reeder formally nominated him as senior pastor of the church.

One member questioned the choice of a man of 58 "who will be with a fewer number of years" in the face of the church's "tradition of long pastorates."

Another called Dr. McKay and his preaching "the greatest blessing God has bestowed on this church in some time."