PRESIDENT REAGAN is apparently inclined to override the objections of two Cabinet secretaries and endorse a plan of the Office of Management and Budget to merge the dam-building activities of the Army Corps of Engineers and the Interior Department's Bureau of Reclamation. A decision by the president to put his political might behind this and other needed changes in resource managment could transform the budget-cutting exercise into a major improvement in natural resource policy.

For decades the rivalry between the corps and the bureau has been the textbook example of bureaucratic overlap and pork-barrel politics. The 1949 Hoover Commission deemed the case for merging the two agencies "overwhelming." Now, with the federal budget in an undeniable state of crisis, the case is even more compelling.

The two agencies theoretically divide responsibilities -- the corps works nationwide on water projects with flood control or navigation as the major purpose, the bureau focuses on irrigation-focused projects in 17 western states. Hydroelectric and water supply projects are up for grabs. The bureau also claims to be uniquely attuned to the needs of western states, but in fact the corps spends almost as much in those states and has field offices throughout the area.

In practice, since most projects are multipurpose, the division of responsiblity has been far from orderly. As the potential for projects shrinks -- there are, after all, practical limits on the number of dams that can be built -- competition for sites has increased. Rivalry between the agencies, each with its own links to powerful congressmen, has also made it impossible for any administration to have a coordinated policy for developing water and agricultural resources.

Direct presidential interest could also breathe new life into OMB's sensible plans to require project beneficiaries to pay more of the cost of constructing and operating water projects. A thoroughgoing policy revision would encompass plans for revamping agricultural programs as well. OMB has backed off its initial misguided proposal to eliminate soil conservation programs. But the budget review of these and other farm subsidies has helped to highlight the fact that many federal resource programs not only waste money, but work at cross purposes.

Better control over the Agriculture Department's watershed projects could save money and reduce overlap with the activities of the corps and bureau. More important would be requiring farmers to take steps to reduce soil erosion in order to be eligible for farm subsidies, and stopping irrigation and other subsidies for marginal grasslands that have been brought under cultivation.

All of these changes challenge traditional ways of doing business in Congress. But feeling is running strong in Congress, even among senators and representatives from states most directly involved, that too much federal money is being wasted and that, even at that, the old policies aren't working.