AS CONGRESS now goes to work on the next budget, Americans are going to find out a lot about themselves and their political ideas. Much casually accepted tradition and received wisdom is coming under fiercely hot challenge. People, not only congressmen but taxpayers and voters as well, are going to find themselves pressed hard to decide what they really think about food stamps, and legal aid, and subsidies for synthetic fuels, and all the rest. On these questions, neutrality and easy detachment will not necessarily be signs of intelligence or devotion to the public interest.

Now that Mr. Reagan has formally sent his budget to the Capitol, a period of rebuttal begins. The interests that built these separate programs will have a chance to defend them. But the crucial decisions are no longer being left exclusively to the subcommittees where the lobbies are strongest. The congressional budget procedures that have been developing since the 1974 reform are changing the nature of budget politics.

The two parties have agreed, in the House, that the tax cut legislation will follow, stage by stage, a reconciliation bill. That's the way the House intends to hold itself to its promise to keep spending cuts running parallel with the tax cuts. A reconciliation bill can be a devastatingly efficient instrument of control. It shifts discretion sharply away from the committees and toward the floors of the House and the Senate -- which are required to vote on limits to spending and the deficit. The reconciliation bill is designed to enforce those limits by assigning each committee a figure, in dollars, that it must not exceed. Each committee will decide for itself how to stay within its total. But the total, once imposed, is fixed. According to the current agreement, that recconciliation bill has to be passed before the tax legislation will be allowed to proceed to conference. It's an extremely promising attempt to ensure that the final budget represents the will of Congress as a whole, rather than the will of certain willful chairmen.

At the end of the present congressinal session next fall, what will have been accomplished? The budget will have been cut, certainly, although perhaps not as much as Mr. Reagan originally hoped. The country will have been through the education that a good hot political fight generates. Perhaps it will turn out that most Americans, when pressed on these questions, decide they don't like some of the cuts that Mr. Reagan and Mr. Stockman have proposed. But the question, throughout the months ahead, won't simply be whether you want the program. The question will be whether you are willing to pay for it with your tax dollars. Remember, the tax cut legislation will stay one step behind the budget legislation on this steep path.

The congressional budget process is a method -- if it works -- to produce a budget with a political base strong enough to support the taxes to balance it. This procedure offers an end to the corrosive practice of passing budgets loaded with spending programs that not many people seem to want, but that no one is able to shut off. It's that kind of spending that has eroded the public's tolerance for taxation, inciting resentment and rebellion against tax rates that keep rising automatically without overtaking the deficit. The goal here is not to cut the budget to any arbitrary figure. The total may turn out to be higher than Mr. Reagan wants, and yet represent a victory for both him and Congress. They will have achieved a political triumph if they can produce a budget for which the country, after careful consideration, is genuinely willing to pay.