WOULDN'T YOU know it? Last Wednesday, the government announced plans to ban most fluorocarbon aerosol sprays - and the next day, Robert H. Abplanalp, the man whose valves made those sprays possible, said a new invention now makes them obsolete. If Mr. Abplanalp is right, the users of such things as hair sprays and deodorants in aerosol cans will be able to go right on using them - as soon as the cans have been fitted out with Mr. Abplanalp's new gadget. And the government's ban will become largely unnecessary.

This is, it seems to us, a fitting last chapter in the saga of the spray cans and the ozone layer. American ingenuity has triumpled once again. Even without intervention by the government, it would have saved us from the dangers that an earlier bit of ingenuity had created. The aerosol cans will remain. The ozone will be protected. The threat of skin cancer will be dimished. Only the fluorocarbons will be gone. And no one will have to give up reliance on aerosol hair sprays or deodorants or antiperspirants or what have you.

The action announced by the government is,of course, proper - with or without a new valve and a new propellent. There is sufficient evidence in hand to demonstrate that fluorocarbons may be depleting the ozone layer. The two-year period over which their use is to be phased out is an adequate response both to that danger and to the pleas of the manufacturers who wanted more time to make adjustments. What is remarkable is the ability of three federal agencies - the Food and Drug Administration, the Environmental Protection Agency and the Consumer Product Safety Commission - to agree on the same program of action. The fact that Mr. Abplanalp has upstaged them by announcing a new valve that permits the use of safer propellents in aerosol cans does not diminsh the importance of their agreement. There are other uses for fluorocarbons, primarily in refrigeration systems, for which regulations still need to be drawn. This inter-agency agreement provides a strong base on which to build those regulations.