POLLUTION DOESN'T pay; polluters do. That is the first point U.S. District Judge Robert R. Merhige wanted to emphasize last fall when he fined the Allied Chemical Company the whopping sum of $13.2 million for illegally dumping Kepone and other chemicals into the James River. The message has not been diluted by Judge Merhige's reduction of the fine to $5 million in return for Allied's donation of $8 million to a new Virginia environmental fund.

It is true that Allied will save a few million this way because the contribution, unlike a fine, is tax-deductible. Even so, the company has now paid the largest criminal penalty ever levied in a federal pollution case. Beyond that, Allied has financed some medical research and cleaning-up in Hopewell, has paid damages of undisclosed amounts to victims of Kepone poisoning - and still faces large civil suits filed by the state and James River watermen. All in all, Kepone's costs to the company - not to mention the human and environmental harm - should be sobering to any corporation that still regards pollution as a nickel-and-dime affair.

This week's events also bolstered Judge Merhige's second point: the polluters should bear at least part of the cost of cleaning up. The judge said last fall that he lacked authority to order Allied to pay part of its fine into a fund for combatting Kepone-related problems. He has achieved about the same thing by forceful persuasion - and the result should be far more beneficial to Virginia than paying the full $13.2 million into the federal treasury. Because the fund will be run by an independent board of citizens, including U.S. Attorney William B. Cummings of Alexandria, there seems to be little danger of it being used for Kepone clean-up work that Allied should finance. Instead, the fund can supplement state and federal efforts to deal with the Kepone catastrophe, and can also help to relieve other major environmental problems in the state. It is a creative, appropriate approach - the one plus, perhaps, that has come out of the whole sad Kepone experience.