Theodore M. Bernstein, 74, an editor of The New York Times and an authority on the English language, died of cancer yesterday at his home in New York City.

Mr. Bernstein joined The Times in 1925 as a copy editor. It was - and is - a job of great importance to any newspaper, because the copy editors are the last to read stories before they are set in type. They see that the stories make sense. They also write the head-lines for them.

Unlike reporters, who get bylines on their stories, copy editors are largely anonymous so far as the public is concerned.

Mr. Bernstein broke out of the largely faceless tradition. Not only did he make important contributions to The Times, but he also became widely recognized through his books as an expert on English usage. His lessons were the easier to learn because his own writing informed by wit and grace as well as by erudition and common sense.

A. M. Rosenthal, executive editor of The New York Times, said yesterday that Mr. Bernstein had been "a guiding spirit" of the newspaper for many years.

"When I was a correspondent for The Times, I always felt he was looking over my shoulder," Rosenthal said. "I wrote for Theodore Bernstein. He shaped this newspaper as much as anyone in its history."

Mr. Bernstein remained on the copy desk of The Times for five years. From 1930 to 1932, he was suburban editor, and then transferred to the foreign desk. In 1939, he became the youngest cable editor in the Times' history, directing foreign news coverage during World War II and its afermath. His next assignment was night managing editor.

In 1951, he was appointed an assistant managing editor. His job was to improve the writing and editing in The Times.

He began writing a regular bulletin called "Winners and Sinners" for the use of Times editors and reporters. He pointed out the successes and failures in the newspaper and the manner in which he did so was a pleasure to read. Mr. Bernstein's bulletins formed the basis for two of his books, "Watch Your Language," published in 1958, and "More Language that Needs Watching," published in 1962.

In "The Careful Writer," which was published in 1965 and which is widely used as a classroom textbook as well as by general students of English, Mr. Bernstein gives several examples of "winners" and "sinners."

"At the risk of outraging contrary opinions - and the risk is formidable when you are dealing with puns - an example of good and bad will be cited," he wrote.

"The first in the opening sentence of a news story about a street corner Kris Kringle who had imbibed too much and fell afoul of the police: 'A Santa Claus carried his load a bit too far yesterday.' The second is a head-line, which will have to speak for itself if it can: "Middies to Have One Bell of a Time Today for Wringing Out Cadets on the Gridiron."

Mr. Bernstein's other books are "Headlines and Deadlines," written with Robert E. Garst, and published in 1933 and reissued in 1961; "Miss Thistlebottom's Hobgoblins: The Careful Writers Guide to the Taboos, Bugbears, and Outmoded Rules of the English Language," in 1973; "Bernstein's Reverse Dictionary," in 1975, and "Dos, Don'ts and Maybes of English Usage," in 1977.

The last book was based on a column Mr. Bernstein wrote three times a week until recently for The New York Times Syndicate, "Bernstein on Words."

In "The Careful Writer," Mr. Bernstein stated his purpose in defending the old ways of the language while making way for the new:

"What good writing can do . . . is to assure that the writer is really in communication with the reader, that he is delivering his message unmistakably and, perhaps, excellently. When that happens, the reader takes satisfaction in reading and the writer takes joy in the writing."

The rules are there, he said, so that we can "express ourselves clearly, precisely, logically, and directly - and to cultivate the habits of mind that produced that kind of expression."

Theodore Menline Bernstein was born in New York City. He was educated at Columbia University and joined the Times in the same year that he graduated from the Columbia School of Journalism.

In addition to watching over the quality of the newspaper, he organized its Paris edition in 1960. He was named editorial director of the book division in 1969.From 1971 until his formal retirement a year later, he was a consulting editor for new operations. But he continued to write "Winners and Sinners" until the end of 1977.

Mr. Bernstein's wife, the former Beatrice Alexander, whom he married in 1930, died in 1971. Survivors include a son, Eric M. CAPTION: Picture, THEODORE M. BERNSTEIN