CLAYTON • The first chapter in what promises to be a prolonged and likely heated debate kicked off Monday with parties on opposite sides of a proposed corporate development staking out their positions on what Mayor Harold Sanger characterized as the “biggest project in the history of the city.”

At issue in the weeks and months to come is a plan that, if enacted, will transform the northeast corner of the county seat into a 6.5-acre Centene Corp. campus.

It was unveiled for the first time before a standing-room-only crowd attending an Architectural Review Board meeting at City Hall. The project calls for a 28-story office tower, retail, residential units, corporate housing and a “civic auditorium” doubling as a Centene training center and a site for cultural events.

Upon completion, the complex will stretch east from the intersection of Forsyth Boulevard and Hanley Road into a section of University City abutting Forest Park Parkway.

A Centene official said the total cost has yet to be determined. Phase 1 could be completed by 2018.