Muslim rebels demanded a $20,000 ransom for two U.N. aid workers they seized in the southern Philippines. In a note sent to the mayor of the town of Masiao, on the island of Mindanao, the rebels said the women, both Filipinas, would be released as soon as the money was received. The provincial military commander, Col. Carlos Pena, told reporters that soldiers have surrounded the area where the two women are being held and were ready to mount a rescue operation if they were not released by noon today. In Manila, meanwhile, President Corazon Aquino vowed to order a sweeping land reform program, limiting holdings to 17 acres, before the Philippine Congress meets July 27. No details were disclosed.