Mark J. Meagher, president and chief operating officer of The Washington Post Co., has resigned effective the end of this year "to pursue other interests," the company announced yesterday.

Meagher, who has been president since November 1977, will continue as a member of the company's board of directors, Katharine Graham, chairman and chief executive officer, said.

No successor for Meagher has been chosen, and Graham said Meagher had agreed to remain through December "to ensure an orderly transition."

In his statement, Meagher, who is 48, said, ". . . despite my love for the people and the company, I feel that I have reached a point in my life where it is time to move on to a new challenge. I am greatly pleased, however, that I will be retaining my ties with the Post as a member of the board."

Graham said that "no one has contributed more to the development of our company over the past decade than Mark Meagher. As general manager of The Washington Post, he led the paper through its most trying hours, and on to new heights of success and profitability."

Graham was referring to a bitter strike by union pressmen against the newspaper that began in October 1975, and lasted into early 1976.

Meagher joined the company in 1970 as a vice president for finance. Prior To that he was an executive vice president of McGraw-Hill Book Co. In 1974 he became executive vce president and general manager of The Washington Post. Two years later, Meagher was appointed president of the newspaper division of the company.

In yesterday's statement, Meagher said, "I have spent an enormously satisfying 10 years with The Washington Post Co., and it is a very deep part of me. For most of this period, I have worked directly with Kay Graham, and I have particularly valued my relationship with her, both professionally and personally."

A company spokesman said Meagher was"looking at a number of things."