By Jonathan Stempel

OMAHA, Neb. (Reuters) - The first question Warren Buffett was asked at Berkshire Hathaway Inc's (BRKa.N) annual meeting on Saturday was whether he was "semi-retired," having given four lieutenants oversight over the company's operating businesses and some investments.

"I've been semi-retired for decades," the billionaire joked. Many in the audience of tens of thousands laughed.

"Warren is very good at doing nothing," Vice Chairman Charlie Munger later retorted. More laughter.

How long Buffett and Munger stay on is more serious.

They have built Berkshire into a $481 billion conglomerate whose dozens of businesses sweep across the American economy. Running it well, and doing a convincing job of it, would challenge many of even the best executives.

Buffett is 87. Munger is 94. And that means change is likely soon, not just for Berkshire, but also for the weekend of events in Omaha, Nebraska, celebrating their accomplishments and values.

"Warren and Charlie remain the principal show, but there is so much more to this culture," said Lawrence Cunningham, a law professor who has written books about Berkshire. "This is not a one-man show or a two-man show."

Buffett and Munger are still responsible for major Berkshire capital allocation and investment decisions.

But in January, Buffett tapped longtime executives Greg Abel and Ajit Jain to oversee Berkshire's business units, making them front-runners to succeed him as chief executive.

He has also for several years given Todd Combs and Ted Weschler some Berkshire money to invest. They could become chief investment officer.

But none has Buffett's and Munger's public profile, magnetism, or history of investing success.

Buffett and Munger took the rare step on Saturday to assure shareholders about Berkshire's future under new leaders.

"The reputation belongs to Berkshire now," Buffett said.

Munger elaborated: "I think we've started something here that will work well enough that it will last. And one of the reasons it will last is, it's not that damn easy to duplicate."

When they're gone, shareholders expect Omaha's largest annual event other than the College World Series of baseball to feel different, with fewer people coming for the meeting and the shopping discounts from Berkshire businesses.

"Crowds will be smaller," said Richard Callahan, a banker at Bank of the West in Omaha.

They're big now.

Last Friday and Saturday at the downtown CenturyLink Center, where the annual meeting is held, the line to buy underwear at the Fruit of the Loom booth sometimes stretched over 120 deep.

Pampered Chef cookware also drew long lines. See's sold most of the 18,578 pounds of candies it brought. Dairy Queen offered 24,722 sweet treats and sold them all.

Across town, Borsheims Fine Jewelry, a Berkshire unit, hosted its Friday night cocktail reception. Ten thousand people were expected.

Karen Goracke, Borsheims' chief executive, said she wouldn't expect Berkshire itself to run much differently under Abel or Jain, whom she has known for a decade.

"People feel like they got to know Warren and Charlie personally," Goracke said. "They feel very connected because they've had years to build that up. I expect there will be some transition. That's just human nature."

David Brown, president of the Greater Omaha Chamber of Commerce, expressed optimism the weekend won't lose its "Road to Mecca" feel.

"We've all seen these iconic leaders in the past, and as soon as they left the companies weren't what they purported to be," he said. "We're not going to see that with Berkshire."

Many shareholders believe they themselves can sustain the weekend.

"The set of values Warren has built within us will carry on for much, much, much, much longer than any one individual," said William Robertson, a firefighter and forester from Switzerland.

"A lot of people here seem to be a familiar face," said Peter Ringsmuth, who owns a publishing firm in Lincoln, Nebraska. "There's some kind of bond."

That's reflected in the nocturnal fortitude of shareholders who line up for the meeting long before doors open at 7 a.m. Saturday.

Robertson said he queued up at 11:30 p.m. Friday.

Jennifer Chu, a technology management consultant from Toronto, showed up at 4 a.m. Saturday, It was her first time seeing Buffett and Munger.

"They're both getting old, and this may be the last time to see them in person," she said. "You never know."

(Reporting by Jonathan Stempel in Omaha, Nebraska; Editing by Jennifer Ablan and Nick Zieminski)