PORTLAND — Teacher strikes drew closer Wednesday in two Oregon school districts, including the largest in the state.Portland Public Schools’ teachers voted to authorize a strike and set a walkout date of Feb. 20.In the southern Oregon city of Medford, teachers said they will walk out at 6 a.m. Thursday if no contract agreement is reached by then.On Wednesday night, a handful of Medford teachers and their union president announced their “utter disappointment” in the day’s negotiations, the Medford Mail Tribune reported. Bargaining resumed Wednesday after daylong talks Tuesday in which a state mediator shuttled between the two sides.Medford Education Association President Cheryl Lashley said bargaining teams would keep trying until a minute before the scheduled strike.Superintendent Phil Long has announced that schools will be closed Thursday.The district’s strike plan calls for classes to be closed through Monday in the event of a walkout. It would then plan to staff the schools with substitute teachers and security officers. All extracurricular activities except high school sports would be canceled.A Medford walkout could involve as many as 600 teachers. Issues include health insurance, retirement benefits, working conditions and salaries.An even larger strike was a possibility in the state’s largest district, Portland, where the teachers union represents 2,900 teachers. The district has nearly 48,000 students.It would be the first such strike in Portland, The Oregonian reported (http://is.gd/KH82XN).