PRESIDENT CARTER'S proposal to bring state governments more deeply into the planning of water projects is a public administrator's dream. Like his recently deceased plan to create a Department of Natural Resources by executive order, it makes perfect sense-in theory. Whether it will seem to make so much sense when the politicians are done with it is something else.

The president wants the federal government to stop paying all the bills, as it now does on most water projects, and to put those projects on a cost-sharing system like that used for major highways. The state would put up 5 to 10 percent of the cost and, in exchange, would share in the decisions on which projects should be built as well as in the revenues they generate.

In a country where federal water projects have been built with little regard for anything besides the clout of the members of Congress whose projects they are, this proposal at least offers a chance for some reasonable planning. State governments are less likely to spend their own tax dollars on extravagant and ludicrous projects than they are to seek federal funds for those things.

Logic argues for the change. States are primarily responsible for water policy inside their boundaries. Yet the federal government has dominated for decades the decisions on which projects are built. The fact that other projects in the same state might be more important has rarely deterred the authorization of whatever projects were on a particular year's list of congressional favorites.

Unfortunately, while some state governments will support this opportunity, others won't.Even the low level at which the president has set the cost-sharing arrangement will be troubling to state legislatures already hard-pressed for funds. And their reaction will be mirrored on Capitol Hill. True, approval of the president's plan would take some pressure off members of Congress to press for unwise projects favored by their constituents. But approval of the plan would threaten to curtail the legislators' prerogative of seeming to send this bounty home from Washington. The question is whether this selfish sentiment will keep Congress from doing something wise.