John Chancellor, who covered 20 political conventions, a dozen space shots and a handful of wars in 41 years at NBC News, died yesterday at his home in Princeton, N.J. He was 68.

The cause was stomach cancer, said his daughter Mary Chancellor Gregory.

A college dropout who left his newspaper reporter's job and broke into broadcasting just as the television age was dawning, Mr. Chancellor was an anchor of "NBC Nightly News" from 1970 to 1982. He appeared first with David Brinkley and Frank McGee, by himself from 1971 to 1976, with Mr. Brinkley again from 1976 to 1979 and alone again until 1982. For most of that time, "NBC Nightly News" was a solid No. 2 in the ratings, behind Walter Cronkite's "CBS Evening News."

It was not apparent from his professorial demeanor and pancake-flat Midwestern intonation, but he said he found presiding over a tightly timed and rigidly formatted newscast profoundly dissatisfying. He stepped aside in 1982, becoming the program's senior commentator and delivering news analyses three times a week until he retired in 1993

"I had money and I had fame," Mr. Chancellor said when he gave up the anchor's chair, "but the last thing I wanted was to be a 65-year-old anchorman. So I decided it was time to take control of my life." He also said he had realized that "I don't want to measure out my life in 30-second introductions to other people who do the reporting."

Still, being an anchor gave him a chance to say his name the way he wanted it said: "Chance-cell-LORE." "In the past," he said, "I was always introduced by someone else, who used the conventional pronunciation, something like 'CHAN-cell-er.' " Drawing out the final syllable matched his conservative-looking image, with his owlish-looking glasses and dark sack suits. "The look," he once said, "of a man who worked for the State Department in the mid-50's and didn't need the money."

He signed on with NBC when network television news was a poor cousin of long-dominant radio networks. Television caught on -- 10 million households had television sets in 1950, his first year with NBC, compared with 87 million in 1960 -- but the technology was primitive. In those days before satellite, the camera crews that worked with him shot 35-millimeter film that took hours to develop. Mr. Chancellor quickly mastered the art of writing scripts that emphasized the power of the images.

But correspondents had to ad-lib when film clips were not ready or when events lagged behind schedule. Once, in 1960, he extemporized for an hour while President-elect John F. Kennedy was shaking hands and hugging well-wishers on the way to a victory party in Hyannis Port, Mass. What set that experience apart from all the other times he went on the air without a script was that Mr. Chancellor's monitor had gone dark and he could not see what his audience was seeing, or what he was describing; a producer whispered the details to him through an earphone.

"It's a little like being a clergyman," Mr. Chancellor said of being an anchor in such situations. "Most of the week you conduct standard religious services, but the importance is when something goes wrong. Right now somebody could come to that door and say: 'A candidate has been shot. Go on the air.' I'd walk in, draw on a lot of experience in this field and ad-lib for five hours."

John William Chancellor was born in Chicago on July 14, 1927. As a teen-ager he went through what he called "oddball jobs": hospital orderly, carpenter's assistant, chemical tester and riverboat deckhand. But what captivated him was an after-school stint as a 14-year-old advertising copy runner for The Chicago Daily News.

"I was dazzled by it at that early age," he said in 1982. "I knew what I wanted." The Chicago Sun-Times hired him as a copy boy in 1947, and he rose through the ranks as a reporter, rewrite man and feature writer. His next job was at NBC's Chicago affiliate, which was then known as WNBQ. The job was tracking down stories in an unmarked mobile unit equipped with a flashing red light and siren.

"For a long time," he said later, "the police thought we were from the Fire Department and the Fire Department thought we were the police. It helped." Once he lay face down in the street and tape-recorded a gun battle between the police and a murder suspect.

NBC soon made him its Midwest correspondent, based in Chicago, and in September 1957, the network ordered him to Little Rock, Ark., to cover the school desegregation confrontation at Central High School there. Little Rock was a last-minute destination. He had been planning to go to Nashville, but caught the last plane to Little Rock instead, arriving in a sport shirt and slacks; he said he had not had time to pack, and each day for a week or so, he bought a new suit at NBC's expense.

One morning, a mob closed in on 15-year-old Elizabeth Eckford, who was approaching the school alone; because of an oversight, she had not been told that the gathering place for the black students had been changed, or that they had retreated when the National Guard turned them away.

"He had wanted a story, a good story," David Halberstam wrote of Mr. Chancellor's reaction to the scene with Miss Eckford, "but this was something beyond a good story, a potential tragedy so terrible that he had hoped it wasn't really happening. He was terribly frightened for her, frightened for himself and frightened about what this told him about his country. He watched in agony."

As the crisis in Little Rock dragged on, Mr. Chancellor often found that he was followed by angry segregationists when he went out to cover a story.

"At first he would panic," Mr. Halberstam wrote. " 'Should I run?,' he would ask himself, but he soon learned merely to keep walking. The locals became angrier and angrier; for television, in particular, was holding up a mirror of these people for the outside world to look at it, and the image in the mirror was not pretty. If you went to the sheriff's office to do an interview, Chancellor remembered, you gave your name and organization to the deputy, who would holler back so the entire office could hear, 'Sheriff, there's some son of a bitch out here from the Nigger Broadcasting Company who says he wants to see you.' "

In 1958, NBC moved him to Vienna, a base from which he covered the military and civilian revolt in Algeria that helped bring Gen. Charles de Gaulle to the French Presidency. A transfer to Moscow followed in 1960, and he covered the trial of Francis Gary Powers, the downed U-2 pilot, and man's first orbit of the earth by Yuri Gagarin, the cosmonaut.

He was named the host of "Today" in 1961, succeeding Dave Garroway, who had been with the ground-breaking early-morning show since its debut on Jan. 14, 1952.

Mr. Chancellor said that by the time he took over Mr. Garroway's grueling routine -- doing two hours of live television every morning -- "Today" was "as well established as Harvard University or Mrs. Grass's Noodle Soup, and it contains elements of both." Under Mr. Garroway, "Today" had tried ratings-raising gimmicks like having a chimpanzee in the studio. But Mr. Chancellor refused to compromise his newsman's role by doing commercials and seemed uncomfortable with the show's softer format.

He certainly was not comfortable with the hours he had to work. He said he once fell asleep on the air on "Today," and in his first week he mangled the name of a guest and the name of the news reader, Frank Blair. "I don't think I'll say who I am because I'd probably get it wrong," he declared. Off camera, he said he had been distracted: he could not remember what day it was, a must for an early-morning anchor.

NBC ended his early-morning misery in 1962, sending him to Europe to cover the Common Market, then bringing him back to this country to cover the White House. That assignment took him to, and got him ejected from, the 1964 Republican National Convention.

Senator Barry Goldwater's conservative supporters were increasingly unfriendly to television reporters, and during a demonstration by delegates, guards ejected Mr. Chancellor for blocking the aisles.

"I've been promised bail, ladies and gentlemen, by my office," he said on the air. His sign-off was, "This is John Chancellor, somewhere in custody."

He also arranged the first joint television appearance of top Israeli and Arab leaders, with Yitzhak Rabin and Anwar el-Sadat. He interviewed every President to serve since Harry S. Truman, every British prime minister since Clement Atlee and other foreign leaders from Khrushchev to the Shah of Iran.

"I got into journalism because I thought I'd have fun," he said. "I found years later that it was also socially useful work. It kind of scandalized my mother and horrified my father, because he said, 'You're condemning yourself to a life of poverty.' And I said I didn't care; I wanted to have an interesting life."

In his final commentary, in 1993, he ruminated about "the change that worries me the most," he said: the isolation of Americans brought about by television and computers.

"Since I joined NBC News in 1950," he said on the air, "the population of the United States has grown by about 100 million people, believe it or not. And yet, it seems to me that Americans don't spend as much time with each other as they used to."

He was honored by the Overseas Press Club of America in 1993 for "distinguished and exemplary service." The award cited Mr. Chancellor's "long-term dedication to presenting the news without the theatrical embellishments used to turn the news into entertainment."

He was the author of "Peril and Promise" and, with Walter Mears, of "The News Business." He left NBC in 1964 to spend two years as the director of the Voice of America.

In addition to his daughter Mary, of Santa Monica, Calif., he is survived by his wife, Barbara; another daughter, Laura Chancellor Archibald of Santa Fe, N.M.; a son, Barnaby John, of Seattle, and three grandsons.

John Chancellor (1927)