Lowell Thomas, the dean of radio news broadcasters who traveled to every part of the globe, wrote more than 50 books, and made a fortune from radio, television, film and real estate ventures, died of a heart attack yesterday at his home in Pawling, N.Y. He was 89.

Mr. Thomas' secretary, Electra Nix, said the former commentator-explorer died "peacefully in his sleep." His second wife, Marianna, was at his bedside.

Mr. Thomas, whose last broadcast was on the CBS Radio network in May 1976, was working on a series of vignettes on what people accomplished in their later years -- what he called "The Best Years" -- for a syndicated radio feature sponsored by Mutual of Omaha.

In the golden days of radio -- before the advent of television -- Mr. Thomas' sonorous voice was known to nearly everyone who listened to a radio. He once had an estimated audience of 20 million for his two nightly broadcasts at 6:45 p.m. EST for the eastern half of the country and 6:45 p.m. PST for the western half.

His invariable program sign off, "So long until tomorrow . . . " was one of the medium's famous tag lines.

Although he was the first person to broadcast news over television (in 1939 for NBC), he never became a television newsman. World War II delayed the development of the infant industry for nearly a decade and a whole new generation of broadcast reporters came out of that conflict. Mr. Thomas did not try to compete with them.

He did, however, produce a television series, "High Adventure," a travelogue that took him and his camera crew to exotic parts of the world. The program ran for three years, 1957 through 1959, on CBS.

It could have been that the hurly-burly of television news dissuaded him. From the mid-1930s onward, Mr. Thomas usually did his Monday through Friday evening reports from a studio next to his home in Pawling, from copy prepared by a staff in New York City, 60 miles away.

Mr. Thomas had attained a sizeable degree of fame some years before beginning his radio newscasts. He was the first reporter to bring the legend-making Lawrence of Arabia before the world, and in doing so, became widely known himself.

He met T.E. Lawrence, the shy British archeologist who led desert Arabs against the Turks in World War I, in Jerusalem after the city fell to the British. He persuaded Lawrence to take him along on his next campaign and filmed Lawrence's guerrilla exploits, obtaining Lawrence's story between battles.

After the end of the war, Mr. Thomas used the film, backed by a symphony orchestra and a lecture-commentary, as a show called "With Lawrence in Arabia." The show drew packed houses around the country and overseas. British audiences totaled more than 1 million. The show was put on more than 4,000 times before he abandoned it.

In 1924, Mr. Thomas put the Lawrence story into book form, using the same title as that of his touring show. The book sold 500,000 copies and went through 30 printings. In 1971, it was rewritten and published for young people.

Lowell Jackson Thomas (he never used his middle name or its initial) was born in Warrington, Ohio, on April 6, 1892. His father, Harry G. Thomas, was a physician and surgeon, and his mother, Harriet Wagner Thomas, was a schoolteacher. When he was a child, the family moved to Iowa and later, in 1900, to Cripple Creek, Colo., then a gold-mining boom town. His father, who had been a schoolteacher before turning to medicine, was a stickler for proper diction, and made his son meet his standards.

Mr. Thomas attended college at Valparaiso, Ind., where he earned a bachelor of science degree before becoming a reporter in his home town. Later, he earned another bachelor's degree and a master's degree from the University of Denver. During that time, he worked as a janitor, a salesman, a short-order cook in a railroad restaurant and a reporter for the Rocky Mountain News.

Then he turned to law and attended Kent College in Chicago while working as a reporter for the Chicago Journal and teaching oratory at Kent. Princeton University followed, where he seemed set on a course of becoming a constitutional lawyer. He also was an instructor in Princeton's English department.

In 1915, between semesters, he made a trip to then relatively uncharted Alaska. He returned from his tour with voluminous notes and pictures, which he made into an illustrated lecture. The law soon was forgotten when the lecture attracted huge audiences, including one at the Smithsonian Institution here.

World War I was raging at the time. Mr. Thomas, who had gained a reputation as a public speaker, was chosen by the Interior Department, with President Woodrow Wilson's approval, to lead a motion picture crew to Europe to film the conflict. Mr. Thomas and his crew covered the war from the North Sea to the Balkans, attached to every Allied army on the Western Front.

In Venice, during the Italian campaign against the Austrians, he saw a notice announcing the assignment of Gen. Sir Edmund Allenby to command of British forces in Egypt. Guessing that the 1917 campaign against the Turks in Palestine was about to intensify, he took his camera crew to the Middle East.

There he met Lawrence, and accompanied him on his final campaigns.

After touring the British Isles with the Lawrence show (which brought Lawrence such unwanted fame on his home grounds that he finally sought anonymity as a Royal Air Force enlisted man), Mr. Thomas continued on around the world. He hunted tigers with the Prince of Wales in India, visited the jungles of Burma and Malaya, saw bushmen in Australia and pygmies in Africa and set the pattern for later peregrinations. He later noted that many of his travels were "on the fringe of exploration."

Mr. Thomas' entry into radio news broadcasting was almost a happenstance. The Literary Digest had dropped the noted war correspondent Floyd Gibbons' program. CBS called on Mr. Thomas to fill the gap. After a week of preparation, the network found that Mr. Thomas' virile, typically American voice and unflustered manner filled the bill. He was an immediate hit.

After a dispute with the Literary Digest in 1932, he switched to NBC, where he was to remain for 15 years. In the 1930s, he covered the coronation of King George VI and reported from Rome and Paris on the mounting threat of another great war.

During World War II, he continued to be one of the most listened-to broadcasters, although challenged by the Shirers, Murrows, Kaltenborns and Trouts, who also had huge audiences. In 1945, he won the DuPont Award for a broadcast made from a P-51 observation plane over burning Berlin.

In 1947, Mr. Thomas returned to CBS, where he was to stay and make news of his own. The then 15-year-old Dalai Lama in 1949 invited him to visit Tibet, long virtually closed to the world. On the return trip, crossing the 16,700-foot Karo Pass leading into India, Mr. Thomas fell and fractured his thigh. Native guides made a litter and carried him for 16 days before reaching the lowlands. Back in the United States, it took an operation to repair the damage.

Although Mr. Thomas, a handsome man of medium height and build who wore a mustache, retained his faithful listeners, his low-key news reports had a relatively small audience among television viewers. However, his format -- leading off with the top news of the day, mixing stories in the middle and closing with something light, either funny or poignant -- is still followed by news broadcasters.

When television began attracting people away from the movies in the late 1940s and early 1950s, one of the devices filmmakers used to try to keep audiences was a process called Cinerama. The innovation used several projectors to give the projected image an illusion of a third dimension. Mr. Thomas produced two of Cinerama's most popular releases: "Seven Wonders of the World" and "Search for Paradise." He also had a large financial interest in radio and television stations in New England and the South.

In 1926, Mr. Thomas and his first wife, the former Frances Ryan, whom he married in 1917 and who died in 1975, bought property in Rockland County, N.Y., in an area known as Quaker Hill near Pawling. There they built a 30-room house. In the 1930s, Mr. Thomas purchased 2,000 surrounding acres. He later developed the area into a rich man's colony of more than 300 large homes and estates.

In 1959, after the Dalai Lama fled to India when the Chinese took over Tibet, Mr. Thomas headed the American Emergency Committee for Tibetan Refugees. His profession honored him in 1964 with the National Association of Broadcasters Distinguished Service Award, and in 1974, he received a special Peabody Award for his long and distinguished news service.

He was an honorary president of the New York Explorer's Club, one of four men to be so honored, including Rear Adm. Robert Peary, the first man to reach the North Pole. Mr. Thomas celebrated his 89th birthday at the club's annual banquet, which named its highest award for exploration "The Lowell," in his honor.

In 1980, when he spent his birthday in Moscow, he was among the first group of Lowell recipients.

CBS chairman William Paley said Mr. Thomas "was a young man 50 years ago when I met him. And he was a young man when I last saw him about a year ago. He represents the early days of radio. The whole industry owes a debt of gratitude for his contributions to our particular means of communication."

Besides his wife, Marianna Munn, whom he married in 1977, his survivors include a son, Lowell Jr., of Anchorage, Alaska, a former lieutenant governor of that state.