BUENOS AIRES, Argentina (AP) _ Argentine polo player Hector Barrantes, stepfather of Britain's Duchess of York, died after a long battle with cancer, the official news agency Telam reported Saturday. He was 51.

Barrantes died Friday at his polo ranch in Guamini, 335 miles southwest of Buenos Aires, the agency said.

He was buried Saturday at Peace Garden cemetery in Buenos Aires.

The Duchess of York, the former Sarah Ferguson, returned to London from Argentina on Thursday morning after a 10-day visit to her ailing stepfather. She made the trip to Argentina with her two children, Princess Beatrice, 2, and 4-month-old Princess Eugenie.

In London, a Buckingham Palace spokesman said she was informed immediately after his death Friday night. ''There is no question of her returning to Argentina immediately,'' said the spokesman, who by custom was not identified.

The duchess is spending the weekend quietly with friends, the spokesman said. Her husband, Prince Andrew, the second son of Queen Elizabeth II, is a Royal Navy pilot currently on duty aboard HMS Campbelton.

Barrantes, born to a poor, working-class family, rose to become a man who was at home with the British aristocracy.

He got his big break at 15 when he was introduced to polo ponies.

He first came to England in 1967 and three years later was employed by Lord Vestey to play polo for Vestey's Stowell Park team.

Barrantes first wife died in a car crash.

In 1974, shock waves flowed through British society when Susan Ferguson, niece of Viscount Powerscourt, left her husband, Maj. Ronald Ferguson, and her daughters Sarah and Jane, to start a new life with her husband's rival on the polo field. The Fergusons' 18-year marriage ended in divorce that year and Barrantes married Susan in a civil ceremony in Argentina in 1975.

Barrantes detected the first warning signs of cancer in September, underwent surgery at a Buenos Aires clinic, and was flown to New York where doctors confirmed he had cancer of the lymph glands.

He underwent chemotherapy before returning to his 1,000 acre ranch, El Pucara, where he bred polo ponies. Barrantes had described his illness as the ''first great inconvenience I've ever encountered.''

In an interview with Hello 3/8 magazine, he said: ''I'm not afraid of dying. Having a clear conscience makes you face death in another way.''

He told the magazine the ranch would eventually be left to the duchess.

''Sarah was there when we started work on the ranch in 1980. We planted the first trees with her. She helped us move over there. Sarah loves the place and in the end it will be hers.''

Despite the rupture in Anglo-Argentine relations following the 1982 Falklands War, Barrantes was welcomed by the queen and Prince Philip to the extended royal family when Andrew married his stepdaughter in 1986.

The duchess was the first member of the royal family to visit Argentina since the war. Argentina and Britain restored full diplomatic relations earlier this year.

Barrantes is survived by his wife, Susan.