By lopping two years off a tentative decade-long contract withSuffolk County’s police union, County Executive Steve Bellone at least has curtailed some of the long-term financial risk the original agreement posed to taxpayers.

But plenty of questions persist. It’s still far from clear whether this contract is, on balance, what the deficit-ridden county needs to put its finances on a more sustainable footing in the long run.

This much is clear: The deal no longer calls for seven years of salary increases as part of a 10-year package that would bring top pay close to $200,000 by 2020. Bellone and the Police Benevolent Association have agreed to pare the deal to eight years overall, with pay hikes guaranteed only for 2013 through 2016.

The revision preserves key gains for the county, including an agreement that newly hired police officers will pay 15 percent of their health insurance premiums — a precedent other county unions supposedly have agreed to accept. The minimum police salary will be frozen at $42,000, and the rest of the PBA pay scale will be stretched for future officers.

To win these concessions, the county gave the union plenty — which Bellone is much less willing to talk about. As of Wednesday, the executive’s office was still refusing to release the county’s memorandum of agreement with the PBA. However, a widely circulated unofficial copy points to several areas of concern.

To begin with, pay hikes would be higher than advertised. Under the revised deal Bellone announced this week, base salaries will rise by a compounded total of 12 percent between June 2013 and June 2016. On top of these increases, however, the leaked memo indicates there will be at least three separate base salary increases starting in January 2013, plus added longevity increments. In addition, base pay will be boosted with a total of 60 hours in added “compensatory time.”

Officers on the payroll in 2014 and 2015 will defer some of that comp time until retirement — at which point the accumulated value will be reimbursable at their final (higher) pay rates, on top of what typically comes to tens of thousands of dollars in accrued sick time. To help retiring cops cope with the tax consequences of their growing severance packages, the county also would agree to create a new tax-sheltered “severance deferral” savings account for PBA members.

Including all the add-ons, it appears total police pay hikes will average at least 4.5 percent a year from 2013 through 2016. Even with offsetting savings on health insurance and a less-compressed pay scale for new officers, will the county’s revenue grow enough to close projected deficits and pay for those raises?

Then there are the intangibles. The county would shift highway patrol functions from less expensive deputy sheriffs back to PBA members. It could never again transfer or subcontract any PBA function to other workers without the union’s permission. And it would pledge not to lay off PBA members.

The leaked version of the agreement further stipulates that these benefits “shall be considered mandatory subjects in all future negotiations.” Under the state Taylor Law, contractual provisions classified as “mandatory subjects of negotiation” are extremely difficult to dislodge or modify. In other words, the PBA would not only gain ironclad job security for cops for the next eight years, it would take a big step toward keeping it forever. Bellone should never have agreed to tie the county’s hands in this manner.

Well before its scheduled vote on the contract next month, the county Legislature should demand — and make public — an analysis evaluating the financial impact of each and every provision, compared both to the current PBA contract and to a theoretical arbitration settlement. Those impacts should be itemized in the context of a multi-year financial plan stretching through the contract’s expiration in 2018. Only then can voters fully weigh the costs and benefits.

If this is truly a good deal, the numbers should bear it out.