San Francisco transit officials are weighing whether to raise Muni fares by a quarter next year, to $3.25. The hike, though small, could be significant: Muni is already one of the most expensive transit systems in the country.

Staff at the San Francisco Municipal Transportation Agency say they need the additional fare revenue to pay for operating expenses, and that the increases would keep pace with inflation. The agency draws at least $200 million a year from fares, and it expects to reap $14 million more in 2021 if fares are increased on all transit vehicles. If SFMTA doesn’t get that money, it may have to slow down hiring of bus and train operators — a dire need as Muni struggles to serve 720,000 weekday riders.

“That’s a conundrum we have,” Chief Financial Officer Leo Levenson told the Board of Directors during its meeting on Tuesday afternoon.

Under the SFMTA’s current budget proposal, cash fares for buses and subways would climb from $3 to $3.25 next year, while Clipper fares would rise from $2.50 to $2.75. The cost of a Muni monthly pass would jump from $81 to $85 next year, and to $87 in 2022. The $40 monthly “Lifeline” pass, for adults earning less than 200% of the federal poverty line, could be adjusted to match fluctuations in Social Security income or the cost of living.

Cable car riders, who now pay $8 a ride, would get the biggest shock. Their fares would balloon to $9 in 2022.

Levenson and his staff will tweak the proposal and bring a concrete recommendation to the board on March 17. The board will vote on the budget in April.

One rider cheered the proposed hikes at Tuesday’s meeting.

“I don’t need a fare cut — my neighbors don’t need a fare cut,” said Howard Strassner. He praised Muni for providing “world-class” service for San Francisco residents.

Yet the increases face stout resistance from within City Hall.

Among the critics is Supervisor Dean Preston, a 26-year Muni rider who takes his kids to school on the N-Judah and rides the 21-Hayes to and from City Hall. Preston ran for office on a platform that included free Muni. Last week, he introduced a legislative resolution calling for a Muni fare freeze.

“I’m a strong believer that we should figure out how to get more people on mass transit, and fare increases do the exact opposite,” Preston said in an interview Tuesday, hours before the SFMTA board meeting.

Preston is drumming up support for a possible November ballot measure to tax businesses and generate funding for Muni, ideally to reduce fares and “get us on a path to free Muni,” he said. He’s drawn backing from at least two colleagues — Supervisors Shamann Walton and Matt Haney both told The Chronicle they applaud these goals.

Members of the grassroots group San Francisco Transit Riders also oppose fare increases, saying they disproportionately burden low-income riders, many of whom pay cash to ride the bus or subway. Muni, like other transit systems, requires people paying cash to cough up the full fare, while offering discounts to those who pay with a smartphone or Clipper card.

San Francisco currently invests $24 million a year in fare assistance programs for needy riders, including free Muni rides for 110,00 low-income youths and seniors, as well as 17,000 monthly “Lifeline” passes. Nonetheless, several people who spoke at the board meeting Tuesday described the cost of Muni as a daily hardship.

“I may have a job, but I don’t have enough (money) to pay for Muni,” said Enrique Santos, who takes the bus each day from his home in SoMa to classes at City College, and to his job as a Starbucks barista. He spends most of his earnings on food and books.

Though the directors expressed sympathy toward low-income riders, they also defended the inflation-based fare increases.

“This policy provides certainty,” board Chair Malcolm Heinicke said, noting that the board, by using inflation as a yardstick, has managed to keep politics out of the process. Other directors agreed, though they expressed sympathy for low-income riders. Only one director, Art Torres, outright objected to fare hikes.

Some riders who spoke out at the meeting said they were insulted and accused the transit agency of gouging customers without improving service.

“You’re charging more for a miserable service, and you’re throwing it on the backs of people who can least afford it,” said Herbert Weiner, a frequent commenter at SFMTA board meetings. “This is a terrible insult,” he added.

Cat Carter, interim executive director of San Francisco Transit Riders, argued that fare increases are failing to meet Muni’s stated goal to boost investment in the system. She noted that the city has steadily hiked fares since 2015, but that SFMTA has lost revenue over that time.

Further complicating matters, the agency is now confronting a fare evasion epidemic that siphons millions of dollars each year, according to Levenson, the chief financial officer. Opponents of fare increases say that Muni will only exacerbate the problem if it charges people more to ride.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan