WASHINGTON - Katharine Graham, the grande dame of modern American journalism who helped transform The Washington Post into one of the nation's top newspapers, died yesterday at a hospital in Boise, Idaho, after suffering a head injury in a fall Saturday. She was 84.

Mrs. Graham, who won a Pulitzer Prize in 1998 for her autobiography, Personal History, was attending an annual conference of business and media executives in Sun Valley, Idaho, when she fell on a concrete walkway outside a condominium.

She had been unconscious since the fall and underwent surgery late Saturday. Her family was at her hospital bedside when she died yesterday.

President Bush paid tribute to Mrs. Graham, whom he called the "beloved first lady of Washington and American journalism."

In a statement, he said: "Mrs. Graham became a legend in her own lifetime because she was a true leader and a true lady, steely yet shy, powerful yet humble, known for her integrity and always gracious and generous to others."

Mrs. Graham's life story, as a soft-spoken and awkward debutante who through personal tragedy became one of the most towering figures in journalism and the first woman to head a Fortune 500 company, was as dramatic as it was inspirational.

Her father had bought the Post in 1933 and later turned it over to her husband, Philip L. Graham. When the dynamic but depressed Philip Graham committed suicide in 1963, Katharine Graham assumed control and did what both her father and husband failed to do - turned the mediocre Washington Post into an American institution.

"She set this paper on a course to excellence that you can't beat," Benjamin C. Bradlee, the Post's former executive editor, told CNN yesterday. "She was the most famous publisher of her day - not only the most famous, but the best."

As president and publisher of the Post during most of the politically turbulent 1970s, Mrs. Graham led the paper through historic decisions that lent it the authority to command sizable influence in the nation's capital.

Defying a court order and the advice of the newspaper's lawyers, she made the bold decision for the Post to print the Pentagon Papers, the government's secret chronicle of the Vietnam conflict.

Soon after, she bore the brunt of the fierce political pressure inflicted on the Post - pressure that included threats from the Nixon White House - during the Post's famous Watergate investigation.

The paper's investigation led to Richard M. Nixon's resignation and made the Post and Mrs. Graham - who would come to be known as the "iron lady" - powerful forces in newspaper journalism.

Arthur Ochs Sulzberger, chairman emeritus of the New York Times Co., said: "Throughout the last half of the 20th century, she used her intelligence, her courage and her wit to transform the landscape of American journalism, and everyone who cares about a free and impartial press will greatly miss her. We certainly will."

Power in Washington

Among her friends and admirers were presidents, prime ministers and princesses, from the Kennedys and Lyndon B. Johnson to Princess Diana and Nancy Reagan, from Henry Kissinger to Gloria Steinem, from Warren Buffett to Truman Capote, who threw his legendary "Black and White Ball" in her honor at New York's Plaza Hotel in 1966.

Even after turning the job of publisher over to her son Donald E. Graham in 1979, and then the chairmanship of the company in the early 1990s, Mrs. Graham was chairman of the Washington Post Co.'s executive committee and remained one of the capital's most famous and influential people.

Her elegant Georgetown home was the setting for some of the city's most power-packed parties, most recently a dinner for President Bush that was seen as the Texan's formal introduction to the town's power elite.

President Bill Clinton dined there after his 1992 election, and President Ronald Reagan was a guest of honor at her home twice.

Mrs. Graham once said that she had considered titling her autobiography Two Separate Lives because her lives before and after her husband's suicide - and her stewardship of the Post - were so vastly different.