Harry Reasoner, whose wry wit and low-key unflappable delivery were mainstays in network newscasting for four decades, died last night at Norwalk Hospital in Norwalk, Conn. He was 68 years old.

He died of cardiopulmonary arrest, said a CBS News spokeman, Tom Goodman.

Mr. Reasoner had been in declining health for some time. He had operations for lung cancer in 1987 and 1989. On June 12, he underwent surgery for removal of a blood clot on the brain, and later developed pneumonia.

Mr. Reasoner, who retired from regular participation on "60 Minutes" on May 19, spent most of his career at CBS News, where he served two hitches as a reporter and correspondent: from 1956 to 1970 and from 1978 to his retirement. From 1970 to 1978, he worked for ABC News, as an anchor of "The ABC Evening News," working at first with Howard K. Smith and then with Barbara Walters.

When "60 Minutes" began in 1968, Mr. Reasoner was an anchor. He rejoined the show when he returned to CBS and remained with it until his retirement, when he became editor emeritus and agreed to appear occasionally. 'Brought the Midwest With Him'

Don Hewitt, the creator and executive producer of "60 Minutes," recalled his long association with Mr. Reasoner and said: "Harry Reasoner was not the only broadcaster from the Midwest, but he was the only broadcaster who brought the Midwest with him to television. He not only had craggy good looks but also that Iowa sense of what's important."

Mr. Hewitt said Mr. Reasoner "was a dream to work with" and "knew what a lot of journalists fail to learn: that everybody needs an editor."

"When Harry was edited, he took it beautifully," Mr. Hewitt said. "His head was so chock-full of ideas that he was never above listening to somebody else."

Dan Rather, anchor and managing editor of the CBS "Evening News" said: "Harry Reasoner was an American original. He was an influential and important voice in American journalism that will be sorely missed."

With his pliancy, Mr. Reasoner nevertheless gained a formidable reputation as a good writer that he kept even when others began writing for him. 'Easy to Write For'

Andrew A. Rooney, who wrote many memorable essays for Mr. Reasoner over the years, said: "I have found in television that it's easy to write for someone who doesn't need you and impossible to write for someone who really needs you. Harry was easy to write for."

Other writers agreed. In the 1960's, when Mr. Reasoner was coming into his own at CBS News, writers highly regarded assignments to any of the programs in which he was involved. He had established a style occasionally verging on impertinence, and he encouraged writers to turn a phrase. If a writer won Mr. Reasoner's approval, it assured a close working relationship with a newscaster who was said to prize good writing above all else.

In contrast to some of his fellow newscasters, Mr. Reasoner said he did not feel that the success of his programs depended on the quality of the visual material.

"The script's the thing," he told a writer who worked for him on the "Sunday News" in the early 1960's. "You give me a literate script, let the camera move in for a tight shot and everything will be fine."

He had a writer transferred from one program when, in one script, the writer referred to the Pope as "the Pontiff," a term that was not only correct but was also used by the CBS News correspondent in Rome.

"A pope is a pope is a pope," Mr. Reasoner said, "and that is what we are going to call him."

Hal Haley, who produced the "Sunday News" during the 1960's, said many would listen for Mr. Reasoner's comments at the end of the program. "They were usually humorous, often poignant, but they were always moving," he said. "People wanted to know what Harry would say, and he never let them down." Career Began in Minneapolis

Harry Reasoner was born in Dakota City, Iowa, on April 17, 1923, the son of Harry Ray and Eunice Nicholl Reasoner. His parents were both educators. His father became a school superintendent; his mother was a teacher. When he was a teen-ager, the family moved to Minneapolis. .

He studied journalism at Stanford University and at the University of Minnesota. In 1943, he entered the Army and a year later won his first recognition as a journalist: first prize in a nationwide essay contest sponsored by the Republican Party. Mr. Reasoner's entry told Republicans what he thought they should do in the postwar years.

After the war, he worked for The Minneapolis Times and became its drama critic. He lost the job, he later confessed, when he gave a touring production of the musical "Up in Central Park" an unfavorable review. In Minneapolis in those days, he said, drama critics weren't supposed to pan touring productions from New York, for fear that they would cross the city off their tours.

At the same time, he produced his only novel, called "Tell Me About Women." Years later, Mr. Reasoner told friends: "It was warmly received. That means it didn't sell too well." When it was reissued in 1964, Mr. Reasoner said he winced at some sentences.

In the early 1950's, he worked as a newswriter for WCCO, the CBS Radio affiliate in Minneapolis, then moved to the United States Information Agency, for which he traveled extensively in Asia. When he returned to the United States, he became news director of KEYD-TV in Minneapolis. From Turkeys to Rebels

He joined CBS News in New York in 1956 and carried out a variety of assignments, ranging from politics to events at Cape Canaveral, at least one Thanksgiving Day Parade and interviews with Fidel Castro's rebels in Cuba.

CBS asked Mr. Reasoner to become co-host of a television show called "Calendar" in 1961, with the actress Mary Fickett. Jack Gould, reviewing it for The New York Times, called it "a delightful oasis of fun and intelligence."

His stature at CBS continued to grow with reports and essays on the CBS "Evening News," "The CBS Morning News," "CBS Reports" and various news specials. But Mr. Reasoner said he wanted to be the anchor for a nightly newscast, and at CBS. Since the network had the services of Walter Cronkite, that was not possible, but he did substitute for Mr. Cronkite on dozens of occasions.

In 1970 he moved to ABC News, where he continued to win plaudits, but not from everyone. Bruce Herschensohn, a special assistant to President Richard M. Nixon, attacked several reporters for "false prophecies" about the Vietnam War, and Mr. Reasoner's name appeared on a list of reporters with whom the White House was especially displeased.

Among Mr. Reasoner's many prizes were two Emmy Awards, a George Foster Peabody Award, and citations from the Society of Silurians, the Overseas Press Club, the Friars Club, the University of Missouri and the University of Minnesota. In addition to his novel, his books were "The Reasoner Report" (1966), "The World Today" (1975) and "Before the Colors Fade" (1981).

His marriage to Kathleen Ann Carroll ended in divorce. He is survived by his second wife, the former Lois Webber, whom he married in 1988, and by the seven children of his first marriage: Harry Stuart, Ann, Elizabeth, Jane, Mary Ray, Ellen and Jonathan.

Harry Reasoner (1923)