History has its moments of exquisite irony, and Washington was filled with them last week.

On one day Jimmy Carter, the president who presided over the disintegration of the Democratic Party's governing coalition, was back in the news. The famous picture of Carter chasing away that nearly mythical "killer rabbit" with a paddle in a pond near Plains, the subject of much derisive comment in the capital as a symbol of his political weakness, was finally printed in the papers. At the same time, on the same page, the press was reporting a plaintive remark by someone else who once figured prominently, but from a different political perspective, in the Democrats' long reign in Washington.

"No intellectual phenomenon has been more surprising in recent years than the revival in the United States of conservatism as a respectable social philosophy," said Arthur Schlesinger Jr., the chronicler of Franklin D. Roosevelt's New Deal, John F. Kennedy's New Frontier and the keeper of the old liberal flame that now flickers so dimly.

On another day the political ironies were more sharply underscored.

Even as the new conservative-ruled Congress was sweeping aside a generation of social programs proposed by liberal Democratic presidents and enacted by liberal Democratic legislators, the preeminent liberal organization that had helped win most of those fights was convening for its national convention in Washington.

Just as the sounds jof jubilation rang out among the victorious Republican ranks on Capitol Hill, delegates from Americans for Democratic Action (ADA) chapters around the country began assembling for their first sessions of the Reagan era.

For liberals of the ADA persuasion this is the hour of adversity. Their critics have been saying for years that their time has passed -- their ideas outdated, their leaders gone, their energies dissipated, their agenda irrelevant, their ideology rejected. Now these arguments have been given tangible form as power shifts to the newly formed conservative coalition on Capitol Hill.

Ronald Reagan today rides as high a conservative crest as FDR and Lyndon B. Johnson did liberal ones at their peaks of popularity.

"If people say that the liberals are outdated and tired, they should at least give the liberals credit for what they've done," says the Rev. Robert F. Drinan, the former Democratic congressman who became ADA's new president last night. "Going way back to the elimination of the poll tax, we've had so many victories along the way. Ours is the tradition that has helped bring about many, many things, like the civil rights bill of 1964, the Voting Rights Act of 1965, the fair housing bill of 1968. ADA goes back to Hubert Humphrey, Dr. Reinhold Neibuhr and to Arthur Schlesinger. Liberals have constructed an America that we know."

But looking back on the glory days of the past offers scant consolation for the liberals of today. Their problem is to find a way to look ahead, and then see if the people are willing to follow where they seek to lead.

Father Drinan, naturally, refuses to accept the demise of the liberals. He sees no permanent political shift to the right. Instead, he argues that people have yet to understand exactly what is being wrought in Washington these dramatic early days of summer, 1981.

Government spending isn't being cut, he says. It's being transferred. "Forty billion dollars from the poor to the Pentagon." Lowering taxes won't solve the economic problems. It will only raise the federal deficits. The quality of people's lives won't be improved.A majority will experience greater difficulties from the cuts in such things as Social Security benefits.

These arguments are familiar. They form the essence of the increasingly bitter Democratic-Republican debate in this fractious capital, a debate now resolved decisively in favor of the Reagan side.

The question is whether that victory represents a permanent defeat for the liberals, the beginning of the long-awaited (and predicted) new conservative era in American life, or a temporary setback in the course of progressive governmental action.

In recent years the nation's policital discourse has been affected by a blurring of terms. Differences between liberals and conservatives became harder and harder to define. That's no longer true. Reagan Republicans know exactly where they stand. They represent fundamentally different values than their political opponents'. In large part because of the GOP's new success, Democrats are now examining their political beliefs as they have not for years.Liberals, too, find themselves forced to spell out clearly where they stand.

Father Drinan again, in a conversation with this reporter:

"An American liberal does not say 'get government off our backs.' He says that government is needed in the economy in certain circumstances. He does not believe in free enterprise, as if that is going to solve everything. He believes that we need the minimum wage, he knows that we need very tough environmental standards and he wants a strong OSHA because there are still thousands of industrial accidents. Furthermore, in the area of helping the poor and the disadvantaged, he believes in the social programs that we have. He thinks that housing is so expensive that virtually everyone needs a good deal of help.

Fundamentally, he believes in government as an entity by which the last and the lowest and the least should in fact be assisted. Likewise, in the area of civil rights and civil liberties, the liberal is the expansionist, if you will, with regard to the Bill of Rights. He would generally believe in enhancing and increasing and inplementing human rights or civil liberties, as the U.S. Supreme Court has done. On the international level, the liberal seeks to carry on that bipartisan consensus that brought about a strong defense with the accent on foreign aid and with a good deal of idealism as well as protecting our interests.

"All of these things are now being challenged. And the liberal, frankly, is frightened."

Fear is something the Democrats, and the liberals, are learning to live with in Washington as the conservatives exercise power denied them for decades. But before awarding them the political future, a caution.

The extraordinary events that tore the Congress last week, stirring angry exchanges and leaving signs of deep bitterness, raised another prospect: that the heavy-handed, hasty and embarrassingly sloppy manner in which the Republicans rammed home their advantage could produce an even stronger, more united Democratic-liberal opposition. What if the conservatives, with victory in their grasp and their liberal opponents reeling from near-mortal blows, overreached themselves at their moment of greatest triumph?

That would be the ultimate in Washington's latest series of ironies.

NOTE: In last week's column on the Supreme Court I stated that other than George Washington, who as our first president named all nine justices, only one president, Franklin D. Roosevelt, with eight, has appointed as many as six to the bench. As Mark Twain might have said, that statement is largely true, with stretchers. That's a devious way of saying I was also half wrong.

The court originally consisted of six justices instad of the present nine, as Michael Henry, an American history teacher in the public schools of Prince George's County, properly points out. Washington named those six justices, and then two more, (plus three chief justices, one of whom was rejected by the Senate). If Reagan names as many as six justices he will, as I said, be eclipsed only by Washington and FDR in the number of such appointments. But thanks for correcting the record, Mr. Henry. The pupils of Prince George's are fortunate to have so careful an American history scholar in their midst.