A city that is cutting its school and public safety budgets while boosting its fees and tax rate might not look like an ideal candidate for a property owner who wants a tax break.

But if the city is Portland and the taxpayer is Pierce Atwood, it’s not as farfetched as it sounds.

The largest law firm north of Boston needs to expand and wants to leave its Monument Square building. It has proposed renovating the Cumberland Self-Storage building on Commercial Street, upgrading its wharf and ground-floor marine amenities while turning the upper stories into a modern office building.

The firm is asking that the city cap its taxes so that it can finance the extensive renovations. While the details have not yet been worked out, this could be a good deal for Portland and its taxpayers for three reasons:

The first is that even with the tax break, a renovated building would generate more taxes than the building would in its current state. It has no heat, no plumbing and no electricity and pays about $17,000 a year in taxes. The renovation would add $12 million to the city’s tax base, and even with the tax break, the city would collect $2.7 million more in new taxes over 20 years than if the building were left alone.

The second reason is that the building’s owner would invest $1.7 million in the wharf and ground floor of the building, improving its potential to support marine businesses and public access to the water. This is an investment that struggling waterfront businesses could not make on their own.

The city would benefit from those improvements, and from the commercial activity generated by what would essentially be a new office building.

The third reason is that it would keep Pierce Atwood in Portland. Losing an important local business would be a blow to the city, and helping it to stay is worth a try.

Even when Portland is cutting back, there are still investments it should be making. This is one opportunity that it should carefully consider.