GARDEN GROVE, Calif. — Robert A. Schuller remembers working hard as a child for his father's fledgling church, cranking out Sunday programs on a mimeograph machine and spending hours tiling the floor of a new church building.

Now, decades later, the younger Schuller is taking on his father's legacy — and adding a few modern twists of his own. Schuller, 51, was installed last month as senior pastor at the 10,000-member Crystal Cathedral in a ceremony beamed live to millions watching the church's weekly televised service, the "Hour of Power."

After years spent in the shadow of his father, 79-year-old Robert H. Schuller, the younger Schuller now faces the weighty challenge of expanding that religious empire. Outside observers wonder if the Crystal Cathedral will continue to thrive without the constant hand of the elder Schuller, whose strong personality and charisma attracted millions of followers with his lively televised sermons.

"The truth is I think a lot of people are questioning whether or not this is going to work," said Gary McIntosh, a professor at the Talbot School of Theology at Biola University in La Mirada. "There's a lot of expectations and a lot depends on whether the congregation there allows him to be himself. He seems a little bit stiffer in front of the camera. He may grow into it, but that's the question."

Part of growing into it will mean staying attuned to a changing audience and keeping the church relevant, said Edmund Gibbs, a professor at the Fuller Theological Seminary.

Gibbs said the elder Schuller tapped into a demographic shift that began after World War II when he moved to Southern California from Chicago in 1955 and started preaching at a drive-in theater. Schuller has said he was at first shunned by his denomination, the mainline Reformed Church in America, for preaching from an outdoor theater.

Schuller exhorted his followers to take control of their destinies with God's help and a positive outlook. That upbeat preaching style made the most of a spirit of change that was sweeping the nation, while Schuller's "drive-in/walk-in church" united California newcomers who craved a sense of community, Gibbs said.

The elder Schuller also did something few other pastors had done so successfully: He studied marketing tactics to lure worshippers from other congregations and built an enormous ministry focused on a generic, feel-good Christianity. That approach, now known as the "church seeker movement," heavily influenced today's most famous pastors, including Bill Hybels, Rick Warren and Joel Osteen, McIntosh said.

The younger Schuller says he's not intimidated by his father's resume and plans to build on his success by bringing the Crystal Cathedral and the "Hour of Power" to even more people.

The younger Schuller began appearing regularly with his father in 2002 after founding a 175-acre branch campus of Crystal Cathedral in San Juan Capistrano.

Although a father-son succession is rare in the Reformed Church in America, the Schullers consider the church a "family business" and the transition has been planned for at least a decade.

The younger Schuller said recent surveys show that nearly half of the far-flung "Hour of Power" viewers consider the weekly broadcasts their only church, so he plans to use Webcams and online courses to help them join the cathedral in the same way locals do.

He hopes to increase cathedral membership to 1 million by 2025, while offering the televangelist broadcasts on iPods and Blackberrys as well as on television and streaming video.

In one of his first sermons after being installed, the younger Schuller addressed the changes by telling the congregation of a recent vision. In the vision, he said, God showed him a potted plant that had stopped drawing water until it was put in a new pot, where it began to thrive.

"In my prayers, I said, 'Lord, that's very comforting,' " he said. "He told me, 'All you need to do is water this plant and feed this plant and it will grow.' God was referring to this congregation."

For his part, the elder Schuller says he couldn't have picked a better successor for the church empire. Now he's focused on creating an endowment with at least $80 million in capital so his son — and those who follow — will never lose it to high land prices.

"Whether he's less than I am or more than I am, I don't know and I don't care. It's a God thing as far as I'm concerned," he said. "I know I did my best and I had to step aside, primarily because he had a calling and I had to give him a power base that would be very, very prominent."