As a cold rain beat against stained-glass windows, more than 2,000 people sat quietly in the neo-Gothic grandeur of the Riverside Church yesterday to hear the Rev. Dr. William Sloane Coffin say goodbye.
In words tinged with sadness, Dr. Coffin delivered his last sermon as the senior minister of the interdenominational church, at Riverside Drive and 120th Street.
''It's finished now,'' Dr. Coffin said. ''Even the unfinished is finished now.''
After a standing ovation, Dr. Coffin stood for a few moments with his hands clasped and with a smile. Then - alone - he walked slowly out of the sanctuary, followed only by the hollow sound of his steps striking the marble floor. Greater Diversity
For a moment, no one moved. A few dabbed at the corners of their eyes.
''It is very sad,'' said 19-year-old Samuel Adams Dexter, a history major at Columbia University who had been attracted to the church, which he joined yesterday, by Dr. Coffin. ''I hope what he stands for won't be diluted now that he's gone.''
Dr. Coffin, who in the 1960's led protests against the Vietnam War and racial segregation, had been at the church for 10 years. There, many say he transformed Riverside, built in the 1930's by John D. Rockefeller Jr., into a more joyful, hopeful place dedicated to a world wracked by inequity and warfare. During Dr. Coffin's years there, the church has become more racially and ethnically diverse and has increased its commitment to helping the poor, from the South Bronx to South Africa.
Early next year, Dr. Coffin, 63, who has been a longtime opponent of nuclear weapons, is to become president of a Washington-based disarmament group, SANE/Freeze. He announced his decision to leave the church last summer. Granting 'Permission'
His sermon yesterday was not fashioned solely as a farewell. He spoke of four tenets of the Christian faith: promise, hope, love and joy, and the need for them. And he cautioned his congregation not to become so pious that they fail to enjoy the world and its creations.
''To suppress joy in life is to produce hatred of life,'' he said.
Then the minister summed up his work at Riverside as having simply given his congregation ''permission.'' Elaborating, Dr. Coffin said he had given people permission to do the things their hearts had been telling them they should do.
In fact, church officials said that Dr. Coffin had infused in Riverside a Christian philosophy that made words and deeds inseparable. If the church believed war was wrong, then the church must actively seek to disarm the world. If racial and sexual prejudice were intolerable, then the congregation should reflect diversity.
But Dr. Coffin's ministry has never had the unanimous approval of his congregation. His ministry, at times, has contributed to discord within the church. Last spring, some detractrors called for Dr. Coffin's resignation because they believed he had become less a minister than an advocate of social and political concerns.
Since announcing his resignation last July, Dr. Coffin has maintained that his departure was not influenced by those who opposed his policies.
A few minutes after the sanctuary began to empty yesterday afternoon, Dr. Coffin and his wife, Randi, met well-wishers in the church's basement assembly hall. Standing near the rear, Dr. Coffin spoke with dozens of people - young and old - who waited in line to see him.
Alyce Mott, who has been attending services at Riverside for the past seven years, told Dr. Coffin that she hoped the world would listen to his message of peace and humanity in much the way his congregtion had.
''I hope so, too,'' he said.