YOU'D THINK IT would be easy to raise three loud cheers for U.S. District Judge William Mehrtens, who ruled on Tuesday that the state of Florida must return to Mel Fisher $2.3 million. The $2.3 million was what the state had claimed as its share of a treasure in gold and silver which Mr. Fisher had dredged up from the Spanish galleon, Nuestra Senora de Atocha, sunk on its way back to Spain in 1622. Mr. Fisher had originally made a deal to give the state of Florida 25 percent of his find. But in an unrelated case, the Supreme Court ruled that the Atocha's waters (beyond the 3-mile limit) were not subject to the state's jurisdiction; so Florida had no case. Yet it continued to claim - in a fine bit of mad logic - that it still had a deal. Mr. Fisher sued, and won. You'd think three cheers would be easy.

Yet there is, of course, another side to these coins. Both the state of Florida and the U.S. government (which also made a claim on Mr. Fisher, and lost) were acting in the interests of their Antiquities Acts, under which historical artifacts, such as those retrieved from the Atocha, are preserved and displayed before the public. Evidently the Atocha's treasure is something to see: a gold and coral rosary, pitchers, cannons, chalices, swords and daggers, muskets, an astrolabe - to say nothing of 7,000 handstruck coins, equally valuable and beautiful. Mr. Fisher may preserve and display his find, or he may sell it off to pay his stock-holders. In terms of public benefit, the hoard might better have been handled by the state the Fed.

And yet again - in terms of good old American pluck and zeal - there can be no question that Mr,. Fisher deserves his find. He has earned it, certainly. Eleven years of searching; three vessels sunk; over $2.5 million spent; and the greatest costs of all, the loss of a son and daughter-in-law who were drowned in the quest. Clearly Mr. Fisher is obsessed - less, probably, by avarice than by some propelling adventurous urge he can't explain himself. In that way he's like the country before it developed the governments which sought to grab his treasure for the common good.

So here's one cheer for Judge Mehrtens and private enterprise; one for the state and nation; and one for Mr. Fisher himself, who will now continue his hunt. Down in the Atocha still, he says, are 896 silver bars, 78 chests of coins and millions in gold bullion - the stuff by which Spain one proved her supreme power in the world.