Catherine McVay Hughes, who led the community board in Lower Manhattan during Hurricane Sandy, supports the outer harbor barrier because, she said, protection measures built solely on the coastlines, yet high enough to ward off the biggest floods, would be unsightly.

“Do we want a 20- or 30-foot-wall between Battery Park and the river?” she asked.

Advocates like Ms. McVay Hughes are attracted to the prospect of an enormous barrier that would protect much of the region. They also say that the use of locally tailored, onshore solutions alone, like berms, wetlands restoration and raised parks, would likely benefit wealthy areas first, not the low-income communities that suffered disproportionately from Sandy in 2012.

But despite its boldness, a barrier like this has alarmed many resilience planning and environmental experts, who say it is an oversimplified, myopic concept that does not attempt to address several major climate threats and could even make things worse.

The Corps’s barrier designs aim to address only storm surges. They would not counter two other climate-related threats — flooding from high tides and storm runoff — and they could trap sewage and toxins, which would threaten the nascent ecological revival of New York’s waterways.

The Corps estimates the wall to cost $119 billion, and it is unclear if the city, New York State, New Jersey and Congress will agree to jointly fund the project, which would take 25 years to build. Even if construction went smoothly, opponents say, the barrier could be obsolete within decades because, they say, the Corps’s estimates of future sea levels are too low.