State lawmakers will need to decide whether to hold property taxes flat or have the option of providing a significant funding increase to public schools, the chairman of the Senate budget-writing committee said Thursday. The remarks added new urgency to an emerging debate over what to do about a decision by the Legislature early this year to ensure that property owners’ taxes didn’t go up in the current budget year just because property values rose. Continuing that policy next year could cost the state more than $400 million, according to state economists.