AS if to dampen any hope of the passage of an agreement allowing the United States to retain a naval base in the Philippines, it rained on Philippine President Corazon Aquino's parade Sept. 10."Let's march to the Senate and shout 'Yes' to the treaty," Ms. Aquino said before stepping off a stage set up in a downtown park and into an crowd of about 100,000. Followed by marchers waving "Yes" banners, Aquino trekked about a mile to the Philippine Senate, where the agreement is being debated. When monsoon rains began pouring down, Aquino donned a white rain jacket while a security officer opened a huge yellow umbrella over her head. Meanwhile, about 15,000 protestors opposed to the agreement gathered a stone's throw away, while a rock band played anti-bases songs. A bus load of Philippine sailors in full riot gear kept an eye on the gathering. "I am for the American bases because America has helped us a lot. If the bases go, the Philippines will be in a lot of trouble," said Alexander Aniag, a driver, as a group of students passed by heading to the anti-bases gathering. "These kids do not know what they are doing." Police say a small homemade bomb exploded under a truck near the Senate, injuring three people. The Philippine Senate began a formal debate Sept. 10 as the demonstrations swirled outside the Senate building. Although the official vote is not expected for a few days, on Sept. 9 a dozen of the Senate's 23 members convinced the Senate Foreign Affairs Committee to put forward a "nonconcurrence" resolution for consideration, effectively guaranteeing a rejection. The agreement must be approved by a two-thirds majority to be binding. Although there is technically no deadline on the Senate debate, the Senate is expected to vote before Sept. 16, when the current agreement which covers US military installations in the Philippines expires. If the Senate rejects the agreement or fails to act before the treaty expires, the US will begin a year-long withdrawal allowed under the current agreement. The US maintains Clark Air Base, Subic Bay Naval Base, and several smaller bases. Diplomats from the two countries signed an agreement on Aug. 27 allowing the US Navy to use the base for another 10 years. Washington announced it would give up Clark Air Base north of Manila, although it was originally included in the negotiations, because volcanic ash from Mt. Pinatubo had made it unusable. Other smaller facilities are to be turned over to the Philippines by Sept. 16, 1992. Opponents led by Senate President Jovito Salonga argue that US bases have perpetuated a "colonial mentality" in the Philippines. Other Senators say they are opposed because the $203 million annual compensation package offered by the US for the use of Subic is not enough.