MANILA, PHILIPPINES — POLITICAL leaders appealed to the Philippine Senate yesterday to ratify a new military bases treaty with the United States, saying it would boost efforts to achieve political and economic stability.Philippine President Corazon Aquino's estranged vice-president, Salvador Laurel, said an abrupt US military withdrawal would create a dangerous security vacuum. "The next 10 months will be a crucial period for our economy. The same goes for our political situation," Ms. Aquino's Executive Secretary Franklin Drilon said. "The ratification of this treaty will help bring us over the hump." Rejecting the accord would send "a strong but wrong signal to the United States" whose help the Philippines needed to pursue its development programs, he said. The treaty allows the US to keep Subic naval base for 10 more years while it gives up Clark Air Base, which has been damaged by eruptions by Mount Pinatubo volcano. The treaty needs a two-thirds majority vote in the 23-member Senate for ratification. Rejection would force the US to withdraw its remaining 8,000 servicemen, ending a near century-long American military presence in the former US colony. At least 12 senators have vowed to oppose the accord, saying the $203 million Washington is offering in yearly security assistance is not enough. They say there are no firm guarantees in US pledges of trade concessions, debt relief, and other benefits. The current US lease on Subic and Clark, America's largest military facilities in Asia, expires Sept. 16. The Senate is expected to vote on the accord next week.