PORTLAND — Cumberland County’s commissioners plan to vote tonight on whether to spend $150,000 for preliminary design work on a proposed renovation of the Cumberland County Civic Center.

The design firm SMRT submitted the winning bid for the design work, which will help the county nail down a cost estimate for the renovation plan.

A county task force has recommended a major overhaul for the 34-year-old arena, from adding club seats and redoing the concession and ticketing areas to enlarging the loading dock and bringing the building into compliance with laws mandating accessibility for the disabled.

Consultants hired by the task force estimated the cost at about $28 million, but the detailed designs are needed to nail down a firm estimate, said Jim Cloutier, one of the three county commissioners. He said the design should be complete this summer, after public hearings are held to allow residents to provide input.

That will give county officials time to determine how much money to ask of county residents, who are expected to vote this fall on a bond referendum to cover the cost.

If the Civic Center isn’t renovated, the task force concluded, the arena will soon attract fewer shows and could lose its prime tenant, the Portland Pirates hockey team.