SEOUL, South Korea — The United States has moved to ease jitters among conservative South Koreans by agreeing to delay the return of wartime control of the South Korean military to Seoul until its forces are better prepared to deter North Korea’s nuclear and missile threats or fight it in a war.

The delay, agreed to on Thursday at the Pentagon, means that the main American military command will stay in Yongsan, central Seoul, for the time being. The United States military’s presence in the heart of Seoul, the South Korean capital, has increasingly become an eyesore, especially among younger South Koreans.

The American military had been scheduled to vacate 653 acres of prime real estate in Yongsan by 2016, relocating most of its personnel there to a new base being built south of Seoul. If the main command post stays on, it will significantly reduce the size of land to be vacated, complicating the city’s plan to build a badly needed municipal park in Yongsan.

“We must deal with this issue in a realistic and coolheaded manner, considering national security,” Min Kyung-wook, the spokesman for President Park Geun-hye, said Friday. Mr. Min’s comment came as the political opposition denounced Ms. Park for breaking her election promise to retake wartime control by 2015.