SAN JUAN, Puerto Rico (AP) _ Pilar Barbosa, a historian and political leader prominent in the movement to make Puerto Rico a U.S. state, has died. She was 99.

Barbosa died Wednesday at Santurce Presbyterian Hospital and was buried Thursday at Maria Magdalena de Pazzis cemetery in San Juan.

Gov. Pedro Rossello declared three days of national mourning.

Cause of death was not given. Barbosa would have turned 100 on July 4.

Barbosa was the daughter of Jose Celso Barbosa, considered the founder of Puerto Rico's statehood movement. She became a well-known figure in the governing New Progressive Party and a respected historian at the University of Puerto Rico.

``The greatest posthumous tribute that our people could render Dona Pilar would be to dedicate themselves to the 1998 plebiscite,'' said Carlos Romero Barcelo, the U.S. commonwealth's delegate to Congress and another ``statehooder.'' The proposed plebiscite would try to determine the future relationship between the United States and Puerto Rico.

Barbosa earned a bachelor's degree in education at the University of Puerto Rico in 1924 and a master's degree in history, international relations and education from Clark University at Worcester, Mass., a year later.

In 1926, she became the first Puerto Rican woman to teach at the University of Puerto Rico and, a year later, established its history and social sciences department.

She wrote more than 20 books, mostly on Puerto Rico's history, received the U.S. Outstanding Leadership Award from then-President Ronald Reagan in 1984 and was active until her death, being appointed official historian of Puerto Rico in June 1993.

``She leaves a void difficult to fill,'' Luis Gonzalez Vales, president of the Puerto Rico Academy of History told The San Juan Star newspaper.