The woman who often served as Cuba's first lady, the wife of acting leader Raúl Castro, is believed to be seriously ill with colon cancer.

BY FRANCES ROBLES

As Raúl Castro rules Havana while his brother Fidel recovers from surgery, Cuba watchers say Raúl's longtime wife, Vilma Espín, is also believed to be seriously ill.

Although there's been no official word out of Cuba, reports of Espín's illness have been making the rounds in South Florida as the woman who often served as the island's first lady misses more and more important events.

Espín has been president of the Cuban Federation of Women for all of its 46 years, and for the first time last month missed its annual anniversary celebration.

The Holguín-based newspaper Ahora recently published a letter Espín wrote for last year's anniversary, suggesting that she was not even well enough to pen a statement this year.

Espín also did not attend the 13th Latin American congress on sexology and sexual education in Brazil, where she was to receive an award. And radio station CMHW in the central city of Santa Clara referred to her last month in the maudlin terms often reserved for the very sick or dead, saying she was the ``eternal guide of the newborn motherland.''

Last month, El Nuevo Herald published a story on the spreading word of Espín's ill health, including one report that she may be suffering from colon cancer.

Raúl Castro temporarily assumed his brother's leadership titles July 31 after the 80-year-old Fidel underwent surgery for intestinal bleeding. Fidel is reported to be recuperating, but Espín's reported ailment might be putting added pressures on the 75-year-old Raúl.

''I have heard she is in fact very sick and is on a respirator, but I have no way of confirming that,'' said Marifeli Pérez Stable, a Cuba expert at the InterAmerican Dialogue, a Washington-based organization. ``I also heard that she asked to be moved to Santiago, where she is from, to die.

``I get this from someone who has contact with well-placed people. I think it's true because of the source, but no one in Cuba is going to say that on the record.''

''She's certainly in very bad shape,'' independent journalist Oscar Espinosa Chepe said by phone from Havana. ''Everyone knows that she is terminal.'' But experts note that Espín has been reported to be very sick before, and in July rumors swept Miami that she had in fact passed away.

''I know that she was very sick on other occasions,'' said Alina Fernández, Fidel Castro's daughter who now lives in Miami. ``Two years ago they said she was very, very, grave, and they were preparing the funeral. I am not sure if she was seen again after that.''

Raúl and Fidel Castro's sister Juanita, a Miami pharmacy owner, said she has heard the same reports about Espín but has not spoken to anyone in Cuba to confirm them.

Espín gained fame in the late 1950s, when she was among the upper-class women who joined the Castro brothers in the Sierra Maestra mountains to fight dictator Fulgencio Batista. She used the nom de guerre ''Deborah'' -- a name she later gave her first daughter.

She and Raúl wed shortly after the revolution's 1959 triumph. Some rumors have them separating some 20 years ago -- in fact some reports claim Raúl Castro has another wife -- but Espín continued in her role as Cuba's first lady. Fidel Castro's own wife, Dalia Sotodelvalle, has never made any official appearances.

''Raúl has always been very protective of Vilma, and used to become angry at Fidel's insistence that she take the role of first lady. He did not like that,'' said Ileana Fuentes, of the Cuban Feminist Network, a Miami-based organization committed to helping women in Cuba become part of civil society. But as she began to weaken and illness began to wear away at her health, Fidel kept insisting.

``That was a source of discord between the two brothers.''

In 1986, Espín became the first woman member of the Cuban Communist Party's Political Buro, developing what Fuentes considers a contradiction between her advocacy for women and membership in the ``old boy's club.''

''She would speak at the United Nations about women's rights,'' Fuentes said. ``But back home Cuban women could not exercise those rights.''

Miami Herald translator Renato Pérez and staff writer Luisa Yanez contributed to this report.