The National Trust for Historic Preservation is warning the city that tearing down the Waikiki War Memorial Natatorium will require a host of costly federal reviews and permits, and says the best option is to rehabilitate the historic site by at least stabilizing the pool and bleachers.

In a letter to the city Wednesday, National Trust attorney Brian Turner wrote, "Significant costs and time would be associated with any demolition proposal in order to properly evaluate the impact to historic properties and the marine environment and to comply with all applicable federal laws."

The letter was a topic of discussion yesterday at the city's monthly Natatorium Task Force meeting. The group, made up of supporters and opponents of rehabilitating the crumbling structure, is charged with coming up with a recommendation for the mayor on what to do with the natatorium.

The task force had its first meeting in May.

It is scheduled to come up with a recommendation by next month.

In his six-page letter, Turner told the city that it would have to overcome significant "legal constraints" before it could demolish the natatorium, including securing two Army Corps of Engineers permits. And Turner told the city that it couldn't assume those permits would be approved, given a slew of laws that would be considered in a review, including the National Historic Preservation Act.

He added that the demolition could also have a negative impact on the environment.

Instead of demolition, the National Trust — a Washington, D.C-based nonprofit dedicated to saving historic places — recommends rehabilitating the natatorium "by, at the very minimum, stabilizing the bleachers and the pool," Turner wrote. "This option would not require opening the pool."

The city put together the natatorium task force following years of back-and-forth over the natatorium's future. A consultant for the city has estimated that it would take $20 million to $30 million to refurbish the historic site, while the price of demolition would range from $1.2 million to $8 million.

Those estimates, though, do not include costs for environmental assessments and permits.

The natatorium has been closed for safety reasons since 1979. Earlier this year, Mayor Mufi Hannemann said he would like to see it demolished and a sandy beach created in its place. The task force was formed to weigh the pros and cons of demolition and to consider other possible options.