The United States, which still has 28,500 troops based in South Korea, has sought to assure its ally that it remains committed to the region as part of the Obama administration’s strategic “pivot” to Asia. But analysts say the fact that senior leaders like Mr. Chung and a handful of influential newspaper columnists now call for the need for “nuclear deterrence,” or at least hint at it, reflects widespread frustrations over the inability of the United States and other nations to end North Korea’s nuclear weapons program. Until recently the idea was too radical for most mainstream leaders and opinion makers, including both deeply pro-American conservatives and nationalistic yet antinuclear liberals.

Advocacy for a nuclear-armed South Korea has been virtually taboo since the early 1970s, when the country’s military dictator, Park Chung-hee, made a serious bid to develop a nuclear weapon, fearing that the United States might pull out of Asia after its defeat in Vietnam. After catching wind of the program, Washington forced Mr. Park, the new president’s father, to stop, persuading him instead to rely on the United States, an agreement that has held ever since.

Mr. Chung and others say that if the United States does not allow South Korea to develop its own nuclear arms, it should at least restore the nuclear balance on the Korean Peninsula by reintroducing American atomic weapons, which were removed from bases in the South in 1991 in a post-cold-war effort to reduce tensions.

Many in the South are now convinced that the North may never give up its nuclear weapons. The South’s new level of anxiety is also apparent in the widespread speculation here about when and where the North might carry out another, non-nuclear military provocation.

North Korea has stoked those fears by saying that on Monday it will drop out of the 60-year-old armistice that ended the Korean War, in a show of anger at new United Nations sanctions for its nuclear test. North Korea has threatened to terminate the armistice in the past, but the greater worry now is that it might take actions to contravene it. There have been cryptic warnings in North Korea’s state-run news media of coming “counteractions,” which have led South Korean officials to warn of an episode like the bombardment of Yeonpyeong Island in 2010.