WASHINGTON—More than a century after blight decimated the American chestnut tree, the U.S. authorities is weighing whether or not to permit a genetically engineered model to unfold within the wild.

The impending choice has unleashed a ferocious debate over the guarantees and perils of genetic engineering amongst legions of chestnut fanatics. Some have been getting ready for years in hopes that a genetically modified tree that can withstand blight will revive once-mighty chestnut forests. Others warn that would have unintended environmental penalties.