With many cities now preoccupied with other crushing costs — pension obligations, retiree health care, accumulated unpaid bills — a sudden call to honor a long-forgotten bond guarantee can be a bolt from the blue, precipitating a crisis. The obligations mostly lurk in the dark. State laws requiring voter pre-approval of bonds don’t generally apply to guarantees. Local governments typically don’t include them in their own financial statements or set aside reserves to honor them.

“These are debts that do not show up clearly, no matter how closely you look at the balance sheets,” said Carmen M. Reinhart, an economist at the Peterson Institute for International Economics who has written extensively about government debt. They “come out of the woodwork in bad times.”

In a number of communities, especially in New Jersey, Michigan and Washington State, local officials have recently scrambled to work out fiscal emergencies caused by guarantees and similar promises. Hoboken dodged a bullet last year, for instance, when a buyer was found for a bankrupt hospital whose debt the city had guaranteed. Buena Vista, Va., narrowly missed a creditor foreclosure of its city hall and police building, after a park authority failed to repay the bonds for a golf course.

In other places, bond guarantees have been time bombs, causing problems too severe to be solved in a workout. Stockton may be headed for Chapter 9 bankruptcy this week after pledging taxpayer money to backstop authorities’ debts for a hockey arena and other showcase buildings. Scranton, a faded former coal center, touched off a full-blown debt crisis this month, losing access to the capital markets when its City Council refused to honor a taxpayer guarantee for a parking authority’s bonds.

Residents of Pennsylvania’s capital, Harrisburg, recently learned from a forensic audit that their city’s fiscal woes could be traced to a guarantee issued in 1998, for the bonds of a trash incinerator project. Every few years after that, the authority running the project issued more bonds, and the city guaranteed those as well.