A nearly three-decade battle to preserve the neglected Wai­kiki War Memorial Natatorium is getting added ammunition from the National Trust for Historic Preservation, which is adding the landmark to its list of "national treasures" — a move that harnesses the support of thousands of preservationists from coast to coast.

Built in 1927, the Natatorium’s memorial arches, 100-meter saltwater pool and stadium bleachers were meant to honor Hawaii’s 10,000 World War I veterans. It has been recognized as an architectural landmark on the National Register of Historic Places and for a few generations was the place where Hawaii residents learned to swim and great watermen like Olympic medalist Duke Kaha­na­moku and his contemporaries trained. However, those glory days ended in 1979 when the Natatorium was closed due to disrepair.

The trust’s new campaign aims to pre­sent alternatives to an $18.4 million plan announced in May 2013 by Gov. Neil Abercrombie and Mayor Kirk Caldwell to demolish the pool and bleachers and develop a public memorial beach at the site, said David J. Brown, the National Trust’s executive vice president, who plans to announce the designation in Hono­lulu on Wednesday.

"The Natatorium is an important war memorial from a period that Hawaii has lost a lot of its history. … It really has the opportunity to be the place that continues to honor the service of WWI veterans," he said. "We think a restored Natatorium could once again become a place of recreation, recuperation and reflection."

Caldwell and Abercrombie have said their plan would be better for the community than spending the estimated $69.4 million it would take to fully restore the memorial.

The Natatorium is the latest on a list of about 45 historically significant places that the trust has made a commitment to preserving in the three years since it began its National Treasures Campaign, which secured $2 million from program partner American Express. "We started the program about three years ago as a way to go deeper and provide more time and staff resources and sometimes financial resources to endangered places," Brown said.

Success stories for trust treasures include Colo­rado’s Chimney Rock Archaeological Area and Paterson, N.J.’s Hinchcliffe Stadium, one of the few remaining Negro League ballparks, he said. In 2012 President Barack Obama established Chimney Rock as a national monument, and the trust’s efforts at Hinchcliffe recently attracted about 700 volunteers who spent a day shoring up the stadium.

By channeling preservation experts and philanthropists nationwide, Brown said, the trust’s treasures have an improved chance of securing government money, grants and private funding. "We almost always can come in and provide a small-size grant to provide planning help and then work on major fundraising to help local groups expand their community of potential donors," Brown said.

The nonprofit preservationist group Friends of the Natatorium began advocating for the historic structure’s restoration in 1986 and had seemed to gain traction in 1995 when the trust listed the structure as one of America’s 11 Most Endangered Historic Places. The designation, which does not have as much teeth as the latest one, led to a partial $4 million restoration by then-Mayor Jeremy Harris.

However, more recently the trust’s efforts had become something of an uphill battle as more key decision-makers in Hawaii came to see the crumbling monument as a safety hazard, whose rust-covered walls blighted Wai­kiki’s shoreline.

Eighty-eight-year-old Fred Wong said he’s optimistic that the new designation will be equally benefical to the Natatorium, which is where he learned to swim as an 8-year-old in 1934 and where he watched exhibitions of his classmate Bill Smith, who later went on to win two Olympic medals.

"We made special memories there," Wong said, adding that his understanding of the Natatorium’s significance deepened after he spent seven years in the military.

Wong, who has shared his thoughts about the Natatorium in an oral-history video proj­ect that will soon be posted on YouTube, said any plan to dismantle the memorial is disrespectful to the veterans whom the Hawaii Territorial leaders sought to honor.

"They wanted to do something really big," he said. "Now we say that was 100 years ago, we can forget about them. … It’s very much like digging up a grave."

But Rick Bernstein, who heads the Kai­mana Beach Coalition, cautions against getting swept up in the "good old days." Bernstein estimates that the coalition has been supporting a new beach as a replacement for the "failed Natatorium structure" for the past 25 years.

"We have supported this change because the only alternative in redevelopment of the Natatorium would be a complete demolition of the structure. City engineers estimate that rebuilding it from the ground up would cost in excess of $70 million, and it would necessitate commercialization of the structure to pay for the phenomenal amount of maintenance required to operate a saltwater pool in the ocean if they could even get a permit," Bernstein said. "The other alternative would be to let the structure continue to cave into the ocean, which would be a risk to life and to the environment."

He said the coalition wants to see the Abercrombie and Caldwell plan, based on the recommendation of the city-sponsored 2009 Wai­kiki Natatorium Task Force, move forward. "Making it a memorial beach rather than a memorial swimming pool is the right thing to do for the people and for the ocean," he said.

In May 2013, Caldwell and Abercrombie proposed razing the swimming pool and bleachers to create open beach space, and moving the arches inland.

City Director of Design and Construction Chris Taka­shige said Tuesday that Caldwell will wait for the results of the plan’s draft environmental statement, which is slated to be completed before the end of 2015, to determine whether the beach expansion plan is the appropriate path forward.

In a statement Tuesday, Abercrombie said, "We are working and coordinating with the mayor, his administration and the City Council to resolve all outstanding issues with the Natatorium as we wait for the results of the environmental impact statement."