Beloved building: The Mariners Medical Arts Center in Newport was designed in 1963 by Richard Neutra. (FILE PHOTO, Daily Pilot / April 28, 2011)

An office developer has finally submitted plans to Newport Beach officials for an addition to an historic building designed by famed architect Richard Neutra.

Preservationists succeeded in preventing the demolition of the Mariner's Medical Arts Building two years ago, and its developer submitted new plans late last month. They would add about 13,000 square feet of office space to the back of one of the structures built in 1963, without destroying the mid-century modern complex.

But activists aren't satisfied.

"Anything being built back there, in my opinion, would ruin the whole spatial quality of the project," said John Linnert, a Costa Mesa architect who spearheaded the campaign to save the complex. "He was a master of designing and composing the materials, but he was also a master of designing and composing the voids."

Built in 1963, the building is tucked into a stretch of commercial properties — at 1901 Westcliff Drive.

An application with the city's Community Development Department, said the developer, John Bral of Westcliff Investors LLC, would build a two-story steel frame office building that would wrap around and about one of the buildings. The first floor would be parking, with the offices above.

Also, Bral plans to replace a staircase that was demolished around the beginning of 2010. Once preservationists discovered that and some other alterations he made, they complained to the city and forced Bral to come up with a plan that would again preserve the historically-significant design. City law requires an environmental review for such changes.

Now that Bral has submitted his building plans, the city will conduct a complete environmental impact report to assess historical, parking, traffic and other consequences of the modifications.

Bral did not immediately return calls seeking comment.