FASTEN your seat belts indeed! The new round of budget cuts planned by the White House would deeply alter the federal role in the American political structure. The proposals, according to some longtime Washington-watchers, could also produce a public backlash against Republican control of the Senate in 1986 and the White House in 1988.
The budget proposals, which are admittedly still in the discussion stage, do represent a starting point in the coming fiscal and tax debate. But the guarded reception that greeted leakage of the plan in congressional quarters, including among many Republicans, should come as no surprise to the Oval Office. The ultimate outcome of the proposals seemed almost implicit in Budget Director David Stockman's opening words reportedly used in outlining the plan: ''Fasten your seat belts.''
Before the congressional budget-cutting session starts up, the engine driving the current plan - the so-called ''freeze plus'' option put forward by Mr. Stockman's shop at the Office of Management and Budget - deserves a major overhaul. Three points warrant comment:
* First, President Reagan is on solid ground in moving forward with a budget-cutting program to reduce federal deficits, projected in the range of $ 200 billion annually over the next several years. That is not in dispute.
* Second, the deficit-reduction effort must be nonpartisan. The public is in no mood for partisanship. If Democrats are asked to join Republicans in enacting a program, the Democrats should not then be put on the spot for doing so in the 1986 elections.
* Third, and perhaps most important, the budget-cutting issue should be intellectually ''neutral,'' to borrow a term that the administration is using to describe its new flat-tax plan - neutral in the sense that (on paper at least) it does not raise more revenues than are currently raised under the existing graduated income tax structure.
When examined in terms of ''neutrality,'' serious questions have to be raised about the new OMB proposals.