Voice of America director James B. Conkling has resigned in apparent frustration over the continuing controversy surrounding the administration's plans to give the overseas broadcasting organization a more combative, anti-communist edge, informed sources said.

Conkling, who became VOA chief last summer, announced his departure in a statement to employes late yesterday afternoon over closed-circuit radio. He said he had "been too many years in the private sector to be able to understand the quite different ways of government workings." The 67-year-old Conkling said he had decided to leave during a visit to his California home last December, and was looking forward to spending more time with his family. He also said he was under no pressure to resign by Charles Z. Wick, director of VOA's parent International Communication Agency, or anyone else, an ICA spokesman said.

Although Conkling did not elaborate on his decision, sources said he had found his effectiveness increasingly impaired by criticism from the political right and left. He has been attacked repeatedly by hard-line conservatives for moving too slowly to transform VOA into an instrument for combating the Soviet Union, Cuba and "Marxist societies."

At the same time, the sources added, Conkling had been unable to overcome the suspicions of VOA career personnel that the administration wants to abandon the agency's reputation for objective news coverage and make it over into an unabashed propaganda instrument.

In January, Conkling provoked rightist political circles when he forced out Philip Nicolaides, a conservative former radio commentator who joined VOA last year and had caused widespread staff concern by writing a memo advocating a strong propaganda role for the organization.

But his tenure also was marked by the departure of VOA's chief news editor, Bernard H. Kamenske, long regarded as the strongest defender of impartiality and independence in VOA's news coverage. Although Kamenske said he left voluntarily for a private broadcasting job, his resignation reinforced the staff's concerns about the VOA's role.