A midwestern banker was asked his views last week about the budget battle back in Washington and the problem of rising federal deficits. He instantly replied: "If we can ever get some statesmanship in the Congress, everything will be all right."

By that, he meant Congress should bow to President Reagan's budget proposals and thus show "statesmanship." In rejecting the president's bidding, the senators who rebuffed his budget approach last week may have failed that citizen's definition of statesmanship. In fact, they demonstrated just what that term means.

Their vote, in another midnight political cliffhanger, was instantly interpreted as the worst setback the Republican president has suffered at the hands of the Republican-controlled Senate. It was that, but also much more.

The vote underscores the increasing political reality that dominates the capital. For all the ideological combat Washington has witnessed since Reagan became president, it has been the politics of the center that has been strengthened.

It is, of course, a tenuous coalition of mainstream Republicans and Democrats that emerges on Capitol Hill. But it is based on solid and potentially lasting ground. In the last year Congress, and especially the Republican-led Senate, has demonstrated its independence from the president on a number of major issues. Sometimes, as in urging that taxes be raised only weeks before the crucial fall congressional campaigns, the Republicans showed true political courage. In other actions, as in the Social Security compromise, members of both parties demonstrated that the congressional process can perform in a positive bipartisan way on a matter of great national concern and political difficulty.

All this should be heartening news for the country, which for too long has been conditioned to think the worst of its national legislators and to despair of the workings of Congress. Yet, ironically, as that Midwest banker indicates, that's not necessarily how people see it.

It has been two years since the federal debt of the United States hit the $1 trillion mark. That figure represents all the expenditure of national treasure for all the wars and depressions and attempts at nation-building, from the settling of the West to the exploration of outer space, since the founding of the country.

In only two years, that national debt has increased by one-fourth again. It has accelerated ever upward and ever more rapidly, at a rate unprecedented in our history. The government's estimates have projected deficits exceeding $200 billion a year, and even rising above $300 billion annually, for the indefinite future. By comparison, the previous single highest annual deficit in peacetime was about $60 billion, recorded in Jimmy Carter's hapless presidency. At the present rate of increase, the national debt will be twice that $1 trillion mark in only four more years. It will soar above the $3 billion mark early in the next decade.

This is not what was supposed to happen. By now, the benefits of Reaganomics enacted by the Congress at the president's urging were supposed to have the nation heading in the opposite direction. The prediction was for a virtual balanced budget in Reagan's third year, with a modest surplus to be achieved in the fourth.

It is that contrast between promise and reality that lies at the heart of the budget debate in Washington, if not throughout the country. Yet that is not how the president chose to frame the debate. His public remarks about the nature of budgets and deficits that preceded the Senate vote have seldom been couched in starker black-and-white terms.

Once again, he employed his "budget buster" analogies and launched his familiar attacks on the "big spenders." It was Reagan vs. Congress, stay on my course or go down the tubes all over again.

"We have sought to reform the spending and taxing excesses that threatened to destroy the American dream," he told the home builders convention here. ". . . But the Congress must work with us to do what is right and necessary if we are to keep those hopes from being dashed on the rocks of partisanship and runaway government spending. If the Congress can summon the discipline needed to rein in the budget monster, we can have the kind of hale and hearty recovery that could become a way of life again instead of just another blip on the boom-and-bust roller coaster of the past."

He spoke about "a lot of moaning about deficits up on Capitol Hill" and said: "If we are to have long-term improvement in interest rates, the Congress needs to join in a bipartisan effort to cut irresponsible spending. Working together, we can and must reduce these intolerable budget deficits that have haunted us for so many years."

They didn't buy it, and not because they are big spenders and budget busters. Quite the contrary. They didn't buy it because they foresaw nothing but greater red ink ahead, further imperiling the national economy.

You can argue about the proper method for reducing the deficits and reversing the upward spiral of debt. Raising taxes just as the country begins to come out of a severe recession could well be the wrong solution, as so many economists are warning.

You can also argue about the proper mix necessary to maintain the nation's military and economic strength. Certainly, Congress has showed its willingness to cut adequately both defense and domestic spending.

But there's little serious argument about the need to move away from the either/or formula, the all guns/no butter approach, being pursued by the president. That was the meaning of the Senate's bipartisan budget vote recorded last week. It was a vote that also carries important lessons for the president:

There now stands in place a growing bipartisan majority that holds the balance of power in the capital. Reagan can bend this group but not break it. Should he fail to heed the repeated message of moderation it delivers to him, he will be in danger of becoming a secondary player in the debates that will shape the country's economic and political future.