One week President Reagan plucks more than $36 billion worth of spending cuts out of a compliance Senate Budget Committee. The next week the Senate virtually rubber-stamps the decision. The third week the once-dutiful Budget Committee rears back and scraps a budget resolution that accommodates the president's entire economic program -- tax cuts as well as spending cuts.

Congress is giving Reagan's economic program a spectacular roller-coaster ride, and if you get dizzy just watching, you're not alone.

To understand what's going on, you need to understand Congress' complex budget process, stripped down to its barest fundamentals:

Each year in the spring Congress is supposed to pass a first resolution that sets spending and revenue targets. Later, shortly before the new fiscal year begins in October, it has to pass a second budget resolution that sets binding spending on ceiling.

As part of either resolution, it can require its legislative committees to cut programs in order to "reconcile" actual spending with budget goals. These are called "reconciliation" instructions.

When Reagan proposed his economic program, the Republican-dominated Senate decided to capitalize on the momentum of his seemingly popular push for spending cuts by acting first on "reconciliation" instructions.

It was a cart-before-the-horse approach, but it got the Reagan program off to a quick good start. Both the Budget Committee and the Senate as a whole easily adopted the instructions, giving the apperance of an easy ride for Reagan.

Troubles came when the budget panel took up the first budget resolution this week. The resolution has to deal with the whole budget, not just spending. It encompasses revenues (including taxes and tax cuts) and deficits (the differences between spending and revenues). It also makes assumptions, often controversial, about how the economy will perform.

As it turned out, conmmittee Democrats objected to Reagan's tax cut and his economic assumptions, while three Republicans, enough to doom the resolution, wanted more spending cuts to assure that the budget would be balanced by 1984, as Reagan has promised. So now the committee will have to try again after the Easter congressional recess.

Meanwhile, the Democratic-run House Budget Committee, which was in less of a hurry to get out Reagan's spending cuts, followed the normal procedure for congressional budgets.

On Thursday, the same day that the Senate committee defeated its resolution, the House committee adopted its version of the first budget resolution, with the "reconciliation" instructions tucked into it. The whole package will go to the House floor after the recess.

At some point, both houses will adopt their own versions of both the budget resolution and the spending cut instructions. Then differences will be ironed out in a House-Senate conference. Then the action will shift to the legislative and appropriations committees. It will be up to them to carry the instruction out.