PORTLAND — Trustees of the Cumberland County Civic Center started the ball rolling on a $33 million renovation project Wednesday, meeting with an architecture firm to look at plans and starting to develop a timeline for construction.

The trustees, who picked the architecture/engineering firm WBRC to do design work for the renovation, plan to hire a construction manager in the next six weeks. Shortly after, Chairman Neal Pratt said, the trustees will decide whether to shut down the arena for an extended period to get the work done quickly or do the work around events, including concerts and the next Portland Pirates hockey season.

Pratt said the trustees will have to weigh the benefits of shutting down the arena, including the likelihood of lower construction costs and the possibility of lower borrowing costs, against the loss of revenue from events.

County voters approved a bond to renovate the aging arena in November. The project includes new entrances to the center, wider concourses and improved concessions, premium seating, arena suites and enhanced back-of-house facilities, including a larger loading dock and better dressing rooms for performers.

Some of the work is expected to start this summer, after a James Taylor concert in late June completes a spring schedule that includes several college and high school graduations in the arena. Don Dethlefts, a consultant working with WBRC, said the Free Street entrance could be rebuilt over the summer without impacting any events.

He noted that concerts tours generally shift to outside venues in the summer, which is considered the offseason for indoor arenas.

But trustees will have to decide whether to push on after this summer and try to complete the project quickly or continue to do pieces of the work over the winter until the schedule is cleared for major construction work in summer 2013.