Halberstam, who lived in New York and Nantucket, Mass., was a passenger in a car that was broadsided by another vehicle in Menlo Park, south of San Francisco, San Mateo County Coroner Robert Foucrault said. He said the cause of death had not been determined but appeared to be internal injuries.
The accident occurred about 10:30 a.m., and Halberstam was declared dead at the scene, Menlo Park Fire Chief Harold Schapelhouman said.
The driver of the car carrying Halberstam and the person driving the car that crashed into his were injured.
Halberstam was being driven by a graduate journalism student from the University of California, Berkeley, which had hosted a speech by the author Saturday night about the craft of journalism and what it means to turn reporting into a work of history.
His wife, Jean Halberstam, said she would remember him most for his "unending, bottomless generosity to young journalists."
"For someone who obviously was so competitive with himself, the generosity with other writers was incredible," she said by telephone from their New York home.
As word of Halberstam's death spread through the news industry, tributes and remembrances poured in.
"The thing about David Halberstam was that he stayed the course, and he kept the faith in the belief in the people's right to know," said George Esper, who spent 10 years as Saigon bureau chief for The Associated Press. "In the end, and I think we can all be very proud of this, he was proven right. The bottom line was that David was more honest with the American public than their own government."
Author Gay Talese, who was at the Halberstams' home Monday night, said he had known Halberstam since the early 1960s, was best man at his wedding and shared Thanksgiving dinner in Paris last year.
"He was a dear friend," Talese said.
Jean Halberstam said her husband was being driven to an interview he had scheduled with Hall of Fame quarterback Y.A. Tittle. Halberstam was working on a new book, "The Game," about the 1958 NFL championship game between the Baltimore Colts and the New York Giants, often called the greatest game ever played, she said.
Halberstam attended Harvard University, where he was managing editor of the Harvard Crimson newspaper.
After graduating in 1955, he launched his career at the Daily Times Leader, a small paper in West Point, Miss. He went on to The Tennessean, in Nashville, where he covered the civil rights struggle, and then The New York Times, which sent him to Vietnam in 1962 to cover the growing crisis there.
In 1964, at age 30, he won the Pulitzer Prize for his reporting from Vietnam.
He later said he initially supported the U.S. action there but became disillusioned. That was apparent in Halberstam's 1972 best-seller, "The Best and the Brightest," a critical account of U.S. involvement in the region.