Ben W. Gilbert, 60, the former director of the D.C. Municipal Planning Office who will leave city government April 6, said yesterday he is "thinking very seriously" of seeking the post of executive director of the National Capital Planning Commission (NCPC).

Rodney Coleman, 40, former special assistant to ex-City Council Chairman Sterling Tucker and at least five others have already applied for the $47,500-a-year job that became vacant Thursday with the retirement of Charles Conrad.

NCPC is a federal agency charged with representing the U.S. government's continuing interest in the development of the nation's capital. The commission has the power to review all city zoning decisions and changes in the city's master plan for development. In addition, it must approve plans for all new federal buildings in the area.

Gilbert lost his job as planning director when Mayor Marion Barry abolished the planning office and created in its place a new Office of Planning and Development.

George H.F. Oberlander, 48, a highranking NCPC staffer, and Ray Nixon, 60, the chief complaint agent for the General Services Administration, who has served on the commission for 10 years, said they had also formally applied for the position.

Reginald Griffith, a planner in private business whose name has also been mentioned as a possible candidate, had no comment.

Although a three-member panel chosen from among the 12 NCPC commissioners will review all applicants, it is understood that commission chairman David Childs, an architect with Skidmore, Owings and Merrill, will make the final selection, an NCPC official said.