THE Philippine Senate will take up debate over a continued United States military presence in the country following Tuesday's signing of a new 10-year agreement.The past year of talks were punctuated by an earthquake, a volcanic eruption, the assassination of Americans by Communists opposed to the US bases, an anti-bases film starring two of the country's senators, and possibly the most intense media campaign here in recent memory. Despite the consensus reached by negotiators from the two countries, the Philippine Constitution requires ratification of the agreement by two-thirds of the Senate to be binding. A century of US military presence in the Philippines could end abruptly if the treaty is rejected. A so-called "nationalist block" in the Senate threatens to scuttle ratification of the agreement intended to replace the current one, which expires Sept. 16. If they are successful, the US would be required to vacate all installations within a year. The new accord calls for a leaner, cheaper US presence: Volcano-ravaged Clark Air Base and several smaller installations would be turned over to the Philippines within a year. Subic Bay Naval Base would remain under US control for 10 years in exchange for $20 3 million a year in direct compensation. If the US is sent packing, Philippine analysts predict the US Congress will begin to whittle away at special trade concessions. As if to demonstrate this, the US reduced the Philippines' sugar quota last month in order to restore South Africa's. But in a call Wednesday night to President Corazon Aquino, President Bush proposed debt relief to sweeten the deal. Investor confidence, already shaky, could erode further. Most analysts here agree the performance of the Philippines' two stock exchanges rides almost exclusively on the outcome of the Senate deliberations. "We're talking about two guys," says a US embassy source in Manila, implying that the US is counting on 14 pro-bases votes. Last month a "straw vote" conducted by Senate President Jovito Salonga, who leads the nationalistic block, showed 16 of the 23 senators opposing the deal. Now insiders say only nine opponents remain. They are expected to argue that the bases perpetuate a "colonial mentality," or that the compensation in the deal is not high enough, when congressional debates begin next week. It is unclear to whom the two anti-base senators are playing. The Filipino people overwhelmingly support an extension of the US military presence, according to a survey conducted by Social Weather Stations, a Manila-based group. President Aquino has appealed on national television and has met with key senators to convince them the agreement is in the interest of the Filipino people. The Armed Forces of the Philippines, largely dependent on bases-related grants from the US to train and equip the country's military, made a rare public assertion of support for the agreement. Military officials are expected to brief the Senate on the merits of the treaty during public hearings starting Sept. 5. Philippine business groups have taken out full-page newspaper ads which point out that the US is the only major Phillipines trading partner that buys more than it sells to the country. Almost all known contenders in next year's Philippine presidential race have expressed support for a bases extension. Other countries in the region have tactfully suggested the Philippines continue to host the bases in the interest of maintaining the region's power balance. But the year-long negotiations have also witnessed emotional anti-American protests. Also, two US military consultants and two US soldiers have been killed by Communist hit-men during the talks. The Communist Party gave further incentive to the Senate to reject the treaty by announcing yesterday it will declare a unilateral cease-fire if the US bases are shut down. Countless debates on the US-Philippine relationship have been held on college campuses and written up by Manila newspaper columnists. Meanwhile the talks snagged on the issue of how long the US should be allowed to stay and demands for higher compensation. By early June, negotiators were within days of finalizing an agreement, according to US embassy sources. But Philippine negotiators held out a little too long. On June 14, Mt. Pinatubo erupted, temporarily halting the talks. The subsequent US compensation offer was reduced because of extensive damage caused by the volcano.