Smith, 26, who sang alto with the group as a boy and left a career off-Broadway two years ago to become the choir's pianist for a tour of China.
"Though we had to face it, no one is invincible," Hamilton said last night. "It is time for a change."
Of his successor, he said: "Jeff is extraordinarily gifted. He was born and raised in the choir; he knows its every fiber."
Parents received the news at a meeting at the group's West Philadelphia headquarters, a former plumbing supply house at 32d Street and Powelton Avenue, which Hamilton bought a decade ago and dubbed "The Embassy."
"I'm shocked, really," said parent Joe Feenane, 56, of Merion. "I thought he would go on for another 10 years, because he is young at heart."
Feenane's 14-year-old son, J.D., has been in the choir for six years.
"Obviously, he feels it's time, so it's time," Joe Feenane said.
The choir, known for its bright-red blazers and eight-part harmony, has been called "America's ambassadors of song."
"We want to make sure the entire season is a celebration of his 36 years," said Stephen Leonard, chairman of the choir's board and a chorale member.
Focused and demanding, Hamilton built the choir from a 30-voice group at Frankford High School to a 140-member troupe of boys and men who travel as far as 100 miles for twice-weekly practices.
About a half-dozen choir members, wearing red blazers, white pants and black tie and shoes, stood to Hamilton's left as he made the announcement.
"I'm happy for him, but then I feel sorry for the kids in the future because they won't have the experience we had," said Kevin Boegley, 14, of Audubon. Boegley has sung in the choir for five years.
Christopher Irving, 14, president of the choir, said he would miss Hamilton's presence.
"He has an air about him," said Irving, of Somerdale. "When he's there you know that you have to respect him."
He has taken the group on 36 international tours, logging more than two million miles and countless adventures, which he will recount in a book he plans to write and title Now What?
He has resisted the trend to turn his boys' choir into a children's choir. "There is a timbre, a color of sound, only a boy's voice creates, a beautiful, almost piercing, crystal-clear sound," he said.
The choir has performed its diverse program - which ranges from gospel to classical - for presidents and the Pope. It has traveled the world to sing in many languages for ordinary folks and a host of dignitaries, including Cuban President Fidel Castro and the late Egyptian President Anwar Sadat, who was so overcome by the choir's performance that he jumped onstage at the end.
Hamilton, whom choir regulars refer as "H," said he is exhausted from years of arranging details, from air travel to cultural indoctrination, buses to concert halls. Hamilton's singers have gone on safaris in Africa, climbed Ayers Rock in Australia, been stranded by an airline strike in Rome, and busted a military curfew in Jordan.
Hamilton is responsible for the safety of his charges, who range in age from 9 to 15. And he takes it seriously.
Last year, on a trip to France, Hamilton took the choir to the beach, lecturing them about lathering up with sunscreen so there would be no sunburns for the performance.
All afternoon, as groups of boys would pass where he was sitting, Hamilton would stop them to issue reminders about sunscreen, recalled Leonard.
One group of boys, however, responded to his harangue with quizzical expressions. "They weren't in the choir," Leonard said. "They were local boys."
The world travel, Hamilton said, is what sets the Philadelphia choir apart.
"We make beautiful music, but our mission is to share with the world and learn about the world," he said. "That's what makes us extraordinary."
It has become increasingly difficult, over the years, to woo the musically gifted. They must audition, pay $600 a year plus travel expenses, and be committed.
"I just have to be stronger than the other influences," Hamilton said. "I'm trying to do for them what my parents did for me."
Hamilton's mother was a pianist who played background music for silent movies at a Pittsburgh theater; his father was a real estate man who rode him relentlessly to practice.
Eventually, Hamilton told his father he wanted to quit. So his father locked up the piano. Two weeks later, he wanted to play again. "Now I had to come back on his terms, and they were tougher," Hamilton said.
A teacher at Carnegie Institute of Technology (now Carnegie Mellon University), where Hamilton earned his bachelor's and master's degrees, urged him to pursue choral conducting.
The choir, which costs about $500,000 a year to run, "consumes my life," he said. Hamilton, who is single, lives in Rhawnhurst and drives a silver BMW convertible with a license plate that reads, DIR PBC. Smith, of Mount Laurel, drives a Sable wagon with no air-conditioning.
His style, too, is different, Smith said. "He's more in their face about getting the job done," Smith said. "I'm more subtle."
Still, he thinks the transition will be smooth. "Choral conducting is my first love," Smith said. "And where better to be than back home where I sang as a boy?"
Contact staff writer Julie Stoiber at 215-854-2468 or email@example.com.
Staff writer Benjamin Y. Lowe contributed to this article.