The start of construction on San Francisco International Airport’s busiest runway Saturday delayed 238 flights, forced cancellations of 97 others, and caused snaking lines of restless travelers.

Construction on the 28L runway, which serves 68% of the airport’s flights, began Saturday morning and is expected to close the runway for 20 days for $17.2 million in repairs, airport officials said.

Chris Morgan, an airport duty manager, said SFO typically sees about 1,200 flights on slow days and up to 1,500 flights on busier days. United Airlines, the airport’s largest operator, was hit hardest, with 66 delays. SkyWest Airlines, which operates under United, made up the bulk of those delays, Morgan said.

Delays averaged two hours, in line with expectations. Delays could worsen Sunday because more flights are scheduled, officials said.

For some travelers, troubles caused by the repairs were a temporary annoyance, but for Dr. William Munn, 54, his delayed flight meant missing a loved one’s funeral.

Munn lingered next to the Delta Airlines ticketing desk Saturday morning after learning his flight was delayed by an hour, which meant he would miss a connecting flight from Atlanta back to his home in Richmond, Va. A few feet away, his wife, Wyndi Munn, was on her cell phone with the airline, trying to get help.

“We’ve had a death in the family, and we’re trying to get back home. It’s not really a great situation,” Munn said. “The Delta representative that my wife is talking to seems to be trying to help, but there isn’t anything that can be done. We’re stuck.”

The Munns joined dozens of other travelers who stood in a weaving line at the airline’s special services desk, where people were trying to swap flights or switch airlines altogether. Travelers settled into leather seats along the windows, made calls on their cell phones to reschedule plans, and kicked their feet up on their luggage.

Saturdays are typically low-travel days, Morgan said, with an estimated 60,000 travelers expected to depart from the airport. That number will probably swell as this week progresses, with the heaviest traffic Thursdays and Fridays.

Dina Hunter, 58, of South Carolina was driving to the airport with her husband in their rental car when they received a notification from Delta that their 1 p.m. flight was now leaving at 2:05 p.m.

“An hour is not a big deal, but it’s a question of whether that is really accurate,” Hunter said as she flipped through a magazine. “It’s unclear if this is a delayed flight or a flight that has been canceled and then rebooked.”

Sisters Shira and Ravit Harari of Israel, whose JetBlue flight to Long Beach was also delayed an hour, said airline representatives did not explain why it was changed.

The two curled up on chairs in front of the JetBlue ticketing desk and said they hoped they wouldn’t miss their connecting flight to New York.

“They just said it was delayed and, ‘We’re sorry it’s delayed,’” Shira Harari said.

Chronicle staff writer Roland Li contributed to this report.

Lauren Hernández is a San Francisco Chronicle staff writer. Email: lauren.hernandez@sfchronicle.com Twitter: @LaurenPorFavor