Dr. Charles A. Sanders, general director of the Massachusetts General Hospital for the past nine years, is leaving that post to become an executive vice president of the Squibb Corporation, the pharmaceutical-based international conglomerate.

His decision, announced at a press conference Wednesday, will leave the top post at the Harvard teaching hospital vacant as of September 1. Trustees of the hospital will form search committee for a successor soon.

Sanders' new job will "make him one of the very top people at Squibb." Ken Rabin, director of public affairs for Squibb, said yesterday at the company's international headquarters in Princeton, N.J.

Sanders' title will be executive vice president for science and administration, and he will be the second-in-command of Squibb International's largest division, E.R. Squibb and Sons pharmaceuticals Rabin said.

He will supervise research and development, drug-testing, legal affairs and administration for the firm, Rabin added.

Sanders will resign both as associate professor of medicine at the Medical School and as a member of the board of directors of the Eli Lilly corporation, a competitor of Squibbs, he said.

Sanders succeeded the late John H. Knowles '47 as head of MGH. Hospital sources said yesterday Sanders was a quiet and efficient administrator, while Knowles was a vocal national spokesman on health care issues. Knowles left MGH in 1972 to head the Rockefeller foundation.

Eastward, Ho.

Sanders told reporters he would pay special attention to developing the market in China for Squibb. He, and Dr. R. Ebert, former dean of the Med School serve on the China Foundation, an organization founded to bring high quality health care to Mainland China. Ebert, now president of the Millbank Foundation, is a member of the Squibb board of directors.

Sanders, who first came to the Medical School in 1958 as a research fellow in cardiology, presided over a successful $114 million fund drive at MGH and negotiated the recent $60-million agreement with the Hoechst Corporation of Germany, the world's largest pharmaceutical company, for research on DNA at the hospital.

Sanders, a specialist in heart disease, said he left the academic and medical worlds "reluctantly."