ST. PAUL, Minn. — Don’t expect the master of ceremonies to get emotional when “A Prairie Home Companion” celebrates its 40th anniversary this weekend.

“I avoid getting choked up. It’s not in good taste,” said Garrison Keillor, humming and snapping his fingers Wednesday as he strolled the Macalester College campus in St. Paul, site of the radio show’s first live broadcast in 1974.

“You never want the audience to be concerned. I coughed during a show in Washington, D.C., recently. People listening at home probably thought, ‘Geez, is this old guy going to croak?’?”

He’s returning to Macalester for a three-day festival marking the anniversary with a three-hour broadcast, a giant singalong, creation of a Lake Wobegon-style “Living Flag” and other hoopla. A Minnesota institution that reaches 4 million listeners, “Prairie Home” has been made into a movie, parodied on “The Simpsons” and graced the cover of Time.

In many ways, Keillor is approaching the party just like any other show – including the fact that, as of Wednesday afternoon, he hadn’t gotten around to writing any material.

“You don’t want to do it too far in advance,” said Keillor. “If you do, it’s hard to get serious about it.”

But don’t let his public persona fool you. A work ethic drives the 71-year-old storyteller to spend about 16 weeks on the road, while also producing books, running his Common Goods bookstore and developing his first play, expected to premiere in late September.