The deal will be worth an estimated $200 million, one of Israel's largest weapons deals with South Korea.
Seoul's media reported that South Korea's Defense Acquisition Program Administration would place the order for two Green Pine Block-B systems by the end of October.
The radars, built by Elta Systems, a subsidiary of state-owned Israel Aerospace Industries, are believed to have a detection range of more than 300 miles. That would cover most of North Korea.
DAPA spokesman King Young-San told reporters in Seoul that the Green Pine units were scheduled to become operational by 2012. "The system will significantly improve our anti-missile defense capabilities," he said.
Green Pine was the winner of a contest that culminated in tests held in August, edging out its main competition from Thales of France.
The Green Pine system will be part of South Korea's Air and Missile Defense-Cell, a missile defense command-and-control center scheduled for completion by 2012.
Elta will integrate the system into the South Korean missile shield, which is based on U.S. interception systems such as the Patriot built by Lockheed Martin of the United States.
The South Korean air force took delivery of the first shipment of Patriot air-defense systems, bought second hand from Germany, in November 2008.
Since then, nuclear-armed North Korea has conducted several missile test-firings, heightening concerns in the south that Pyongyang was becoming more aggressive amid political uncertainty about what is happening in the hermit regime.
North Korea is believed to possess some 600 Scud ballistic missiles capable of hitting targets across South Korea and possibly parts of Japan.
Pyongyang also has an estimated 200 Roding-1 missiles that could reach Tokyo.
The North has also carried out a series of tests on its long-range Taepodong-2 missile, most recently on April 5 over the Sea of Japan.
Since then, North Korea has fired more than a dozen missiles and detonated its second nuclear device in defiance of international opposition, prompting the U.N. Security Council to impose sanctions in June.
Israel's Haaretz newspaper reported Friday that South Korea was also discussing with Israel Aerospace Industries the possibility of buying the Arrow-2 missile defense system.
India and Turkey have also expressed interest in the Arrow. India has already acquired Green Pine.
However, Haaretz defense analyst Yossi Melman noted, "The chances are slim that a foreign country will purchase the Arrow before a joint Israeli-American missile development occurs."
The United States has provided the bulk of the funding for the Arrow program.