YOU NEVER know just how long it takes a good idea to become a perfectly reasonable law in Virginia, but maybe 35 years is enough time. That's how long members of the General Assembly have been discussing -- and then dismissing -- proposals to let voters elect local school boards if they so choose. Longer ago than that -- 1947, in fact -- Virginia actually gave Arlington County the authority to elect its school board members. Everything was all right for a while, but when the Arlington school board decided to resist "massive resistance" to desegregation of the public schools in Virginia, Richmond lowered the boom on any elections of school boards. Ever since, there have been just enough members of the legislature around to kill even the most modest attempt to revive the idea of elected school boards. The old familiar excuses for maintaining this ban are sure to be trotted out again this year, but there is one small, promising note already: a House of Delegates committee has voted 11 to 8 for a bill that would give at least some voters a chance to experiment.

This latest proposal would let voters in Arlington, Fairfax and Prince William counties and in Virginia Beach decide whether to elect their boards directly instead of allowing county boards to appoint the members. Alexandria might be added to this list through a floor amendment being considered by Del. Marian Van Landingham. The House committee bill would allow 10 percent of the registered voters in any one of these localities to petition for an elected school board. The question then would go before the voters in a referendum in November 1992. If approved then, the elections could be held in 1994.

How's that for a wild and crazy, permissive bit of legislation? All it allows is an option for a tiny fraction of the state to decide whether it might like the elections idea. If any locality prefers its appointed board, that's what it could keep on having. Three years ago, when the legislature was talking about this, Prince William County Sen. Charles J. Colgan observed to his colleagues that "the people were wise enough to send us here. We should be wise enough to let them elect their school board members." But a good question then as now is whether enough of this wisdom exists among the lawmakers. If not, maybe those voters will have the wisdom to send some legislative replacements to Richmond this fall.