The Salt Lake City Redevelopment Agency has changed its mind about how to design a public building on downtown's Block 57 and will tear down part of a structure already in place.

The change, approved by the agency's board of directors last week, may cost taxpayers $273,156 extra, according to estimates.But redevelopment officials said it will make the building architecturally consistent with the rest of the block.

The block, between 200 South and 300 South and between State and Main streets, has been a source of criticism in recent years. The Redevelopment Agency owns nearly all the block and is building a public plaza near the recently completed 24-story Utah One Center.

The most recent changes concern a two-story activity building being constructed in the middle of the plaza. The building will house offices for the plaza's administrators and will include areas the public can rent for special events. An outdoor stage will be on one end of the building, and a police substation on the second floor.

The Redevelopment Agency's board approved a design for the building last year, but Director Alice Steiner said those plans weren't entirely consistent with the design of the rest of the plaza.

BRW Inc., a Minneapolis firm hired by the agency as consultants on the block's design, recommended the changes, she said.

Steiner said the agency knew last year, before construction started, that it might have to make changes. But it decided not to delay the project.

"We chose to move ahead instead until we could get a more coherent idea of how the block would look," she said.

The changes will extend a barrel-shape exterior on the second floor from one side to the other and will move the location of the police station toward the center of the building, among other things. Some of the steel pillars already in place will be removed and reconstructed.

The agency gave its board of directors, which is composed entirely of City Council members, three options for changing the building. The cost of those options ranged from $225,028 to $380,914. The board chose a middle option.

Agency officials said the extra costs may be lower than estimated.

"When I asked for the estimates, I said I don't want any surprises," said Valda Tarbet, the agency's project manager. "These estimates are maximized, not minimized."

Tarbet said the extra costs are offset by $195,000 the agency has been able to save on the block by reducing landscaping and using cheaper materials for minor items.

The change isn't the first extra cost. The parking garage beneath the plaza already cost millions more than expected because the agency didn't begin designing the plaza until after a private developer started building the garage.

Earlier, redevelopment officials were criticized for buying out all business owners on the block in hopes of putting together a sweet deal for a developer. But one business owner refused to sell and won a lawsuit against the agency.