In the cave of the winds, as they impolitely used to call Congress, the debate was proceeding as usual. The words echoing through the chamber were apocalyptic (we were going to destroy ourselves economically and militarily), the speakers were drawing sweeping historical analogies (the most revolutionary budget this nation had ever seen), and the seats and aisles of the deliberating body were the same as ever (largely empty).

But this was not business as usual. All around was evidence of historic change -- the forlorn demonstration, billed as a massive protest march, that in size and emotion and effect turned out to be a pale imitation of the great protest rallies of the past; the air of resignation and defeat that hung over the ranks of the Democrats; the exultation and eagerness that marked the triumphant Republicans as they rushed to embrace, with all the ardor of the true believer, the unproven economic plan that would set the nation on a dramatically different course.

Nothing understood the sense of old and new political currents flowing through the Congress and nation beyond more, though, than the separate appearances of two opposing politicians. One, Delbert Latta of Ohio, spoke with the authority of victory; the other, Thomas P. (Tip) O'Neill Jr. of Massachusetts, expressed the bitterness of the vanquished.

Latta: "As I say, the American people want tax relief and they want tax relief now. They want relief from inflation. They want it now. They could not care less about economic assumptions. They want action by this Congress, and by golly I think this Congress is prepared to act."

O'Neill: "The difference in these bills is basically this: Do you want to meat ax the programs that have made America great or do you want to move slowly and say, if there has been a mistake, if we have been wrong in this program, we can come back. You close the door on America with the Latta bill.

"I ask you this, bear that in mind. I have been in public life for 46 years and the day that I have to look at the next election, instead of looking at America, then I do not want to be in public life. I hate to think in my heart that in the members of this body there would be such shallowness."

But much more than shallowness lay behind the vote that fashioned this political sea change. Hard political realities were being faced.

Butler Derrick is one of many Democrats who anguished over his vote. He's a young congressman from a rural South Carolina district along the Georgia border who has been intimately involved in the budget battle. Long before Ronald Reagan's election signaled a new political wave sweeping over the Democratic South, Derrick's political opponents had accused him of being far too liberal on such issues as abortion and prayer in public schools. They also said he was too close to Jimmy Carter. He is, in fact, a moderate who wants to remain a Democrat -- and a congressman. How he resolved the conflicting forces swirling around the budget struggle was neither shallow nor unusual.

"I've been here since 1974 under Presidents Ford and Carter and I've never seen an operation as well orchestrated as the way the Reagan administration has handled this budget battle," he said the day before the vote.

The president invited me down to the White House one morning with five other congressmen. It was very pleasant conversation. There wasn't any pushing. He was giving his views -- kind of a good-guy conversation. They have apparently gone back through my contributor files and pulled off prominent conservatives that have contributed to my campaign over the years and also probably have supported the national Republican ticket. They have gotten in touch with them.

"It's been very effective in the business community. I would say that probably 60 or 70 percent of the large business people in my district have contacted me. And of course I have had many small businessmen contact me. I don't recall that I've ever been lobbied quite as hard from the district. Usually my district doesn't get too involved in this sort of issue. But they have this time, and it's obviously coming from a well-orchestrated effort."

Reaching his decision meant reacting to other pressures and considerations. He's refreshingly candid in expressing them.

"I consider practically anything I do 50 percent politics and 50 percent being a congressman, but you cannot divorce the politics from any decision I make.

"What I've tried to do is look at both budgets, I start out as a Democrat wanting to support Democratic programs, wanting to believe they're in the best interests of the people I represent. And having served on the Budget Committee for four years I was right familiar with it. So I started out kind of in neutral, leaning toward the original [Jimmy Carter] Democratic initiative. Then [House Budget committee Chairman James R.] Jones came along with his budget, and of course Gramm-Latta evolved out of the Reagan administration as a supposedly non-partisan budget. Well, in looking at it in detail there's not a great deal of difference between them. As you well know, the real decisions will be made this summer under the appropriations process. And there's enough flexibility in the budget process. aSo if you decide that, and that your constituents are going to be just about as well off under one as the other -- or at least there isn't any substantial difference that will affect my district, and the country, of course -- then you look at the politics of it.

"And the politics of it are: rightly or wrongly -- and I think rightly probably -- Reagan is perceived back home as being the one that started all this budget cutting. You can talk about Reagan and you can talk about Jones, but the average fellow will tell you that if it hadn't been for Reagan there wouldn't be a Jones. They're probably right. We've had all sorts of conservative proposals to come before Congress that were not here a year or six or eight months ago. They're here because Reagan was the catalyst. Most people I talk to, and I think they're right, back in the district, say, 'You know, I don't know if he's right or he's wrong, but I'm not pleased with what we've done up to now, so I say let's give the guy a chance to see if it'll work.'

"Frankly, from a Democratic viewpoint, it's a smart thing for us to do.

"You know, if it works we're all better off and we're glad we've done it. If it doesn't work, then we can correct it. But we can correct it and say, 'We've given the man his chance -- and it doesn't work.' If we pick it apart now we'll never have that platform to go back to. This is kind of the way I've reached the decision.

"I've had a lot of pressure on me, I'm considered, I guess as a member of the Rules Committee, part of the Democratic leadership and I have had a good bit of pressure put on me from members of the leadership and what not. And I've just explained it to them. Quite frankly, to vote other than to vote for Gramm-Latta, which I plan to do, would be like throwing gasoline in the face of my constituents."

Demise of the Democrats, a modern retelling of Death of the Republicans, installments 1936 and 1964, is the current bestseller in Washington. It could become a classic, or another instantly produced and quickly forgotten tome.

From the Democratic perspective, perhaps the best analysis of the shockwaves created by last week's big Capitol Hill vote came from what would seem to be an unlikely source -- Jimmy Carter, the Democratic president the beleaguered Democrats like to forget.

Carter broke his silence and drew a lesson for his party by citing the example of Harry Truman. In a speech Friday in Truman's hometown of Independence, Mo., Carter said:

"As in Harry Truman's day, it is a difficult and challenging time to represent the people's interests in public office. Well-heeled lobbyists still haunt Washington seeking favorable treatment at the expense of the general public. Fringe political groups use scare tactics to intimidate those who disagree with them. And now there is a heightened skepticism about what government can or should accomplish. There are even those who argue that the main business of government should be to do nothing -- to abandon those who need help or to retreat from the field of political battle, especially on the most controversial and vital issues. These voices are not new; for the time being they are only louder.

"Some of the critics simply do not have faith in democratic government, because they fear the exercise of the public will -- the demand for justice and broader economic opportunity.

"Harry Truman always remembered that our nation's best investment was in people. He had to struggle for success, and he appreciated government at all levels and its responsibilities in overcoming obstacles to personal achievement. He was never reluctant to use government forcefully when necessary to pursue the public good. He was proud of tight budgeting and the elimination of waste, but these goals were not considered to be ends in themselves. They merely permitted government to do a better job of what was right and what was necessary."

Carter believes Truman's "ultimate goals were the same ones that still guide our Democratic Party and most other Americans." After last week's vote, that premise now faces its severest test.