Henry Grunwald started working for Time magazine as a part time copy boy in 1944 after graduation as a Phi Bet? Kappa from New York University.

'I didn't intend to stay . . . I thought of it as an interesting job, with a chance to write letters and make telephone calls," Grunwald recalled yesterday.

But Grunwald also started doing something that didn't endear him to some of the magazine's writers: As he carried their prose around the office, he found ways to improve upon their writing. He started rewriting, part of the job description for a Time editor, and some of the editors were impressed.

Now, in an era when copy boys have become copy persons, Grunwald has been selected to become editor-in-chief of Time Inc., starting next June 1. He will be only the third editor to have such a title-the others being cofounder Henry Luce and Hedley Donovan, whom the 56-year-old Grunwald will succeed.

Donovan, the editor-in-chief since 1964 who plans to retire next summer, announced Thursday that he had recommended Grunwald as his successor. "Henry started here as a copy boy. Let all copy boys, or copy persons, take heart," Donovan said in a memorandum to the magazine company's staff.

In a telephone interview, Grunwald said yesterday that he "doesn't see why not," when asked if a young copy person today could reasonably aspire to his prospective high editorial office.

At the same time, Grunwald said the main reason why Time magazine has survived and continued to thrive since it was started in 1923 is because "it fulfills a very useful and necessary function . . . it organizes the news in an accessible way."

He compared the weekly news magazine to an encyclopedia, in the sense that Time follows a principle of organization, of seeking to portray some order "out of the chaos . . . of everything that's going on." Critics of Time in previous years said the magazine tried to impose its own ideas of order-or those of Luce-on its readers.

But under Grunwald, who became managing editor of Time in 1968 and served in that capacity until 1977 nthe longest tenure for any Time M.E.), the stridency that critics previously found objectionable disappeared and he began to overhaul the magazine-adding enviroment, energy, behavior and the sexes as new sections, issuing special editions, expanding the use of color photography and-most recently-redesigning typographical layout.

Since stepping down as Time managing editor in late 1977, Grunwald helped reorganize Fortune magazine from a monthly to twice-monthly publishing schedule.

When he succeeds Donovan next summer, Grunwald will assume editorial responsibility not only for Time and Fortune but also for the company's other magazines-Life, Sports Illustrated, Money and People, as well as Time-Life Books Inc.

Time's board also approved Donovan's recommendation that Washington-native Ralph Graves, 54, become editorial director of Time Inc.-effectively Grunwald's deputy. Graves formerly was managing editor of Life and has been with the publishing company for 30 years.

Both Grunwald and Graves will become directors of Time Inc., which has grown from the small magazine venture of Luce and co-founder Britton Hadden into the largest magazine company in the country as well as a major pulp-paperboard-building materials firm and owner of cable television operations, The Washington Star newspaper, and the Book-of-the-Month Club. Revenues of the firm now exceed $2 billion on an annual basis.

Donovan, who will be 65 years old nex May, is a native of Minnesota. He was a Rhodes Scholar at Oxford, a Washington Post reporter from 1937 to 1942, and a Navy intelligence officer before joining Fortune as a writer in 1945. He became Time Inc. editorial director in 1960 and editor-in-chief in 1964 at the recommendation of Luce.

A native of Vienna, Austria, Grunwald came to the U.S. when he was 17. He wrote 30 cover stories for Time before becoming the youngest person ever to serve as a senior editor.

Grunwald said yesterday that he considers his greatest contribution, while Time managing editor, was "much more original reporting than before." He explained that the early concept of Time was as a "summary of the news . . . drawing on existing newspapers for much of the material . . . but it became obvious over the years that a mere . . . digest was not adequate."

On other subjects, Grunwald said:

No significant changes now are being contemplated for Time but rather a period of refining developments of the past decade.

Time Inc. currently is experimenting " in a low-key way" with development of a new science magazine. A previous attempt to develop a specialized women's magazine "didn't come up with the right formula" and although such a publication is a future possiblity it is not now under active consideration.

"I am reluctantly for" a Carter administration legislative proposal to prohibit police forces from conducting surprise raids on newsrooms. Enactment of any press related law acrs to reduce press freedom but the search issue is "fairly horrendous," he said, referring to a Supreme Court decision earlier this year that innocent parties are not immune from surprise searches.