ONE OF THE most entrenched and least defensible of American public policies is the federal government's subsidization of maritime interests-- shipowners, maritime unions, shipyards. Fortunately, the Reagan administration may be beginning an effort to turn all this around.

It is a long way from intentions to results, and the report submitted by Transportation Secretary Drew Lewis to a Cabinet council actually proposes strengthening some benefits, while it would weaken or eliminate others. But there is some promise in the Lewis proposals as reported in The Post last week.

The key point is that Mr. Lewis is evidently prepared to withdraw support from one of the three principal maritime beneficiaries--the shipyards--while maintaining or increasing some benefits for shipowners and maritime unions. The maritime lobby has been so successful in part because it has stuck together: the three support the same congressional candidates, especially members of the maritime committees, and the same measures. But Secretary Lewis would reportedly favor merchant ship owners at the expense of U.S. commercial shipbuilders. Direct subsidies to shipyards would end. Cheaper foreign-built ships could be registered in the United States, and U.S. ships could be repaired abroad without payment of the current 50 percent tariff.

Unfortunately, the secretary proposes other measures to help shipowners that would cost consumers or taxpayers more than current law does. He would require more cargo between U.S. ports, including the Virgin Islands with their oil refineries, to be carried in U.S.-registered ships. He would exempt U.S. seamen's wages from income taxes, giving them a quick windfall that their unions can crow about, and in the long run benefiting the shipowners, who can pay lower wages.

In other areas Mr. Lewis' proposals move in the pro-competition direction that has characterized much transportation policy in both the Carter and Reagan administrations. Mr. Lewis would eliminate federal regulation of domestic cargo rates. He would authorize a fleet of "defense-relevant multipurpose carriers," owned by the Defense Department and leased to shipowners. This fleet would undercut the maritime lobby's traditional argument that the subsidy system is needed to maintain a sealift capacity in American hands for emergency use. The secretary would not authorize subsidies for ships not already in operation, which suggests he may be looking toward some distant day when operating subsidies are phased out by attrition.

It is true that these plans have not even been formally presented. But that they are attributed to as politically canny a Cabinet member as Mr. Lewis gives hope that the administration will begin the long overdue work of dismantling the system of maritime subsidies.