Philippine President Gloria Macapagal Arroyo ended months of speculation and uncertainty Saturday by announcing that she will run for president in next year's elections.

Mrs. Arroyo, 56, a staunch U.S. ally in the war on terror, announced last December that she would not run for president in the May, 2004 elections. She said she would use her remaining time in office instead to concentrate on political reforms and on wiping out the endemic corruption that has traditionally plagued the Philippines.

On Saturday, Mrs. Arroyo told a rally of 20,000 supporters that she had changed her mind: she will run for a full six-year presidential term next May after all. The U.S.-educated economist said she had changed her mind because she now has the necessary experience to do what is needed to reform the country's economic and political policies.

Mrs. Arroyo, who was elected vice president, took over the presidency in January 2001 after then-president Joseph Estrada was forced to resign amid massive protests against the corruption in his presidency. He is now on trial for plunder, a capitol offense in the Philippines.

Although Philippine law allows for only one six-year presidential term, Mrs. Arroyo is free to run because she was never elected president. In July, Mrs. Arroyo's government put down a rebellion staged by around 300 soldiers who accused her government and the military of corruption. She said the uprising was part of a larger conspiracy to topple her government.

Last week, Vice President Teofisto Guingona and the Senate majority floor leader, Loren Legarda-Leviste, both resigned from her Lakas political party.

Mr. Guingona had earlier resigned from Mrs. Arroyo's cabinet, protesting that she was too close to the United States, the Philippines' former colonial master.

Mrs. Arroyo's critics have also complained of her decision to allow American troops onto Philippine soil, to train their Filipino counterparts in counter-terrorism techniques in the war-torn southern province of Mindanao. Surveys have shown Mrs. Arroyo's popularity flagging of late. Ironically, in light of her earlier promise to root out corruption, she has been hounded by accusations that her husband, lawyer Jose Miguel Arroyo, is himself guilty of corruption. Her administration has also been plagued by continued restiveness in the military.