THE LAST LEGAL rockfish hole in Maryland is Washington's own Potomac River, and it appears it will stay that way at least through this summer.

The tidal Potomac legally is Maryland water, but because the river borders Virginia as well and fishermen from both states use it, its resources are overseen by a bi-state commission. The commission has determined in its wisdom to permit rockfish fishing in the Potomac starting June 1, despite the statewide moratorium imposed by Maryland.

This sounds simple enough, but now Maryland's legislature has approved a ban on possessing rockfish in the state, except for commercial operations processing fish caught legally in other jurisdictions for transportation and consumption out of state.

When you boil the fat out of all that legal mumbo jumbo, you are left with this: You can catch rockfish legally in the Potomac River but if you bring them back to Maryland, you're breaking the law the second you set foot on land.

Just how carefully the law is going to be enforced will be interesting to watch, particularly since commercial watermen, who may catch hundreds of pounds of rockfish in the Potomac, will be perfectly within their rights to land the fish in Maryland for export to other states, while some poor sport fishermen standing alongside with one rockfish will be in violation of the law.

One reason the Potomac commission voted to permit continued rockfish fishing is the Potomac's healthy state, by comparison with other Bay tributaries. Rockfish and their cousins, white perch, have continued to flourish in the river, which has less pollution than others because it isn't a dump for industrial waste, there being little industry on its banks, and because Blue Plains and other sewage plants on the Potomac are held to higher effluent standards than others hereabouts.

Rockfish are reasonably plentiful in the Potomac as far upstream as Washington, where the better anglers at Fletcher's Boat House near Chain Bridge regularly bring home stringers-full. The District still lacks a fisheries management plan or enforcement people, so you can catch anything you want in any amount in District waters.

Below Washington, the commission has imposed a five-fish-per-day limit on rockfish, and no fish smaller than 14i or longer than 34i can be kept.