When negotiating its current contract with the city, the Portland Police Association did something clever. To avoid sticker shock over a substantial pay increase, the union settled on a modest 2 percent hike—and agreed, instead, to pad officers' checks with a series of difficult-to-track premiums rewarding things like longevity, physical fitness, college degrees, and a willingness to work odd shifts and holidays.

Those benefits, some of which we wrote about last March, are coming back to bite Portland City Council—and will complicate Mayor Sam Adams' pledge to close the city's $17.4 million budget deficit without having to lay off any cops from the city's wealthiest bureau.

According to a fresh city analysis of the police bureau's $126 million operating budget, just two of those perks—payouts for working holidays, and extra pay for having a long career—have combined for $1.9 million in unexpected costs. That's significant, since the bureau is looking, in a best-case scenario, to cut $6 million next year, crossing its fingers that enough cops will retire (56) so that it won't have to lay any off.

How did those surprises arise? Here's what financial planners say:

• Longevity pay (2% after 15 years, 4% after 20, 6% after 25 years) has been budgeted within premium pay but [it] expenses within salaries. Unfortunately, the bureau has fully expensed its premium pay budget, meaning that the bureau has systematically under budgeted personnel by about $1.3 million.

• A new 2011 contract provision deferred holiday payouts which were previously lost if not used. This new contract provision was not flagged as an added cost during negotiations but in practice appears to be driving up current year costs by about $600,000.

The whole analysis (yes, it's dense) is worth a read. It's a roadmap that balances where the bureau would like to head against the harsh truth of a difficult budget season. Beyond ferreting out the hidden costs, it frets that the bureau has been cutting its equipment budget for too long by too much, worries that not enough cops will retire to avoid layoffs or a fresh infusion of cash, and suggests the bureau trim its spending on Hooper Detox and its Service Coordination Team treatment program for addicts.