Maj. Gen. Robert C. Kingston, commander of the 2nd Infantry Division in South Korea, has emerged as the prime candidate to take over the Rapid Development Force, Pentagon sources said yesterday.

Kingston, if the Army gets its way, will succeed Marine Lt. Gen. P. X. Kelley, whom President Reagan recently named to become assistant Marine commandant, effective July 1.

Under the gentlemen's agreement reached by the Joint Chiefs of Staff, Kingston would command the RDF for the next two years and then be succeeded by a Marine general.

There has been a good deal of inter-service rivalry over command of the RDF. The prevailing argument in backroom meetings at the Pentagon, sources said, was that any U.S. military action in the Persian Gulf within the next few years would involve putting soldiers or Marines on the ground, with the Navy and Air Force playing supporting roles. That argument calls for an Army or Marine general to command the quick-reaction force.

Although Kingston still must be formally approved by Defense Secretary Caspar W. Weinberger and Reagan, none of the other services has proposed a competing candidate, putting the Army general out in front.

Kingston, 52, would be taking over an organization in transition. The administration has told the Joint Chiefs to scrap Weinberger's timetable of turning the RDF into an independent command over the next three to five years. The new goal is to push through this evolution in about 18 months.

Once it becomes an independent command, the RDF commander could obtain forces like the 82nd Airborne Division or a Marine amphibious force by sending the request straight to the Joint Chiefs, bypassing the U.S. Readiness Command bureaucracy that oversees such matters now.

Kingston is a specialist in the kind of unconventional warfare that might break out in the Persian Gulf as the scramble for oil and other resources there intensifies. After commanding the 3rd Special Forces Group at Fort Bragg, N.C., Kingston ran two different brigades of the 1st Air Cavalry Division in Vietnam from 1969 to 1970. He ran the John F. Kennedy Center for Military Assistance at Bragg from 1975 to 1977 and has been commander of the 2nd Infantry Division in Korea since May 1979.