STARTING IN SEPTEMBER, diplomats and employees of foreign governments will have to pay tuition to send their children to public schools in Montgomery County - even if they are county residents. This scheme, recently concocted by the Montgomery County School Board, is being hailed as a way to avoid budget cuts, the tuition is expected to bring in about $3 million each year. While it may offer the school system another way to raise money without raising taxes, the plan is unfair.

Board members contend that diplomats are draining the school system's budget because they are exempt from paying sales and income taxes. They argue that tuition would simply make up for tax revenue the county couldn't otherwise give to the schools. But employees of foreign governments who pay property taxes - the single largest source of revenue for the school's budget - will be charged partial tuition as well. The argument is that those diplomats don't pay enough taxes, so the school system is entitled to a little more money from them.

School board members are kidding themselves if they believe that this plan is reasonable. Once they start requiring certain county residents (but not others) to pay to attend public schools, they go well beyond the question of legitimate cost-savings and get squarely to the issue of how "public" the education actually is. When the seven-member board - three of whom have just been elected - convenes in early December, it should come up with a formula for charging tuition to all who live outside county lines and send their children to the county's schools - and leave it at that.