When the city manager of troubled Stockton, Calif., had to tell city council members why it was on track to become the biggest American city yet to go bankrupt, it took hours to get through the list.

There was the free health care for retirees, the unpaid parking tickets, the revenue bonds without enough revenue to pay them. On it went, a grim drumbeat of practically every fiscal malady imaginable, except an obvious one: municipal pensions. Stockton is spending some $30 million a year to pay for them, but it has less than 70 cents set aside for every dollar of benefits its workers expect.

Some public pension experts think they know why pensions were not on the city manager’s list. They see the hidden hand of California’s giant state pension system, known as Calpers, which administers hundreds of billions of dollars in retirement obligations for municipalities across the state.

Calpers does not want cities like Stockton going back on their promises, and it argues that the state Constitution bars any reduction in pensions — and not just for people who have already retired. State law also forbids cuts in the pensions that today’s public workers expect to earn in the future, Calpers says, even in cases of severe fiscal distress. Workers at companies have no comparable protection.