BLOOMBERG WINS ON SCHOOL TESTS AFTER FIRING FOES
New York City's Panel for Educational Policy approves Mayor Michael Bloomberg's plan to impose strict promotion rules for third-graders, but only after he and Staten Island Boro Pres James P Molinaro fire and replace three members just before vote; photo of Chancellor Joel Klein and others at vote; Bloomberg defends unusually muscular use of power now that education administration is accountable to mayor, saying his representatives must vote for what he believes in; students scoring at lowest level in English and math tests will have to repeat third grade unless they improve after summer school or teachers appeal; 15,000 of 74,000 students could be affected; Bloomberg emphasizes determination to end social promotions; critics say retentions most affect black and Hispanic children, who often lag behind whites and Asians (M)