Two Communist rebel suspects were arrested in connection with last month's slaying of three Americans near Clark Air Base outside Manila, police said. One of the men has admitted serving as a lookout for the Oct. 28 murders and named others allegedly involved, police added. At least 13 suspects were still being sought. In three separate attacks, two American airmen, a retired U.S. sergeant of Filipino descent and a Filipino national were shot and killed. Police said the confessed accomplice told investigators that the killings were carried out by the Communist New People's Army to retaliate for the airlifting by U.S. Air Force helicopters of three Filipino policemen wounded in a clash with rebels on Sept. 18.