IT WAS NICE to see Mr. Nixon at the White House Again. Even the most Democratic guests at the dinner were delighted at the opportunity to snub the ex-president (Mrs. O'Neill had a lovely time), and the rest of us can be relieved at this further confirmation of the differences between the United States and the Soviet Union.

In 1965 Mr. Nixon went to Moscow, and was treated with all the respect owed to an ex-vice president. He asked to see Nikita Khrushchev, who was living there in internal exile, a special Russian limbo, and was told that it was impossible. Nothing daunted, he slipped away from the KGB one evening, drove to Khrushchev's apartment, and rang the bell.

They wouldn't let him in (you never escape the KGB), so h epushed a note through the door, presenting his respects, as a gesture to the man who had, after all, started detente between the two countries with the "spirit of Camp David" and the test ban treaty.

For the Soviet government, however, Khrushchev was a nonperson. He had been driven from office in disgrace, and had ever since then been the victim of as much vilification as could safely be heaped upon someone whose name wa never mentioned in public.

Foreigners find thisRussian habit of pretending that their former leaders never existed both absurd and repugnant. Now it is true that 1965 was the year after Khrushchev's fall and it might be argued that Brezhnev and Co. were justified in wanting to keep him out of sight. But Khrushchev is now dead and buried, and Brezhnev and Co. still ignore his career, as they still ignore trotsky, Bukharin and Stalin.

The Republican Party, in its heart of hearts, would liek to pretend that Nixon never existed, either. His name was on theparty ticket five times, but it was never mentioned at their 1976 convention. Presidet Ford invited him to none of the bicentennial celebrations (just as Brezhnev invited Khrushchev to none of the 1967 celebrations marking the 50th anniversary of the Russian Revolution), and GOP leaders were horrified to learn that President Carter had invited him to meet Teng Hsiao-ping.

He exists, for all that. No amount of anathemas or imprecations will make him go away or wash out his role in American histroy. He disgraced the presidency, but Watergate did not cancel his election or obliterare his administration. He has at least as much right to a White House invitation as Shirley McLaine.

MUCH THE SAME point occurred last year when some bright sparks in the Immigration Service decided to try to deport a Vietnamese general who had been photographed shooting a prisoner during the 1968 Tet offensive. Some people thought that he had no business here and should be shipped back to Saigon, where he would be disposed of properly.

The same people made a great fuss in 1975, when the Vietnamese refugees came pouring into the country. It was alleged that America was no place for the defeated politicians, generals, police and so on, especially those among them who did not always abide by the Geneva convention.

President Ford and Secretary Kissinger found the liberals' objections disgraceful, and were themselves roundly attacked for the word. But disgraceful it was: They were America's people, and a country cannot turn its back on its past without disgracing itself.

They were America's clients, allies, suppporters and friends. Presidents, Congresses and people had supported them for years, encouraging their resistance to the communists. America did it, not comspiracy of Lyndon Johnson and Dean Rusk, and these unhappy refugees were therefore the responsibility of all Americans, including Anthony Lewis and Mary McGrory.

During the late 19th and early 20th centuries, the British imported large numbers of Indians to East Africa to run their new colonies there. When these colonies kwere given their independence in the 1960s, the British were faced with the question of what to do with the Indians, who sensibly feared that their prospects were not good.

They were given British passports and in due course the governments of Kenya, Uganda and Tanzania started to expel them. Their fate was inescapably a British responsibility. Various British governments did their best to escape it, of course, and there were many who urged the dishonorable course of disowning these people.

In the end, ungraciously, the British government bowed to the inevitable, did its duty and admitted the East Africa Asians. They hated doing it, and the whole business is a shabby and discreditalbe episode.

The father have eaten sour grapes and their children's teeth are set on edge. A country cannot escape its history. It will be another couple of generations before the Germans are fully trusted again in Europe, the British have to live with the disagreeable legacies of their empire and the Americans have to put up with Richard Nixon and Vietnamese ex-generals.

ENOUGH is enough, however. Countries are responsible for their past, but there must be a cut-off point somewhere and countries that are obsessed with their history tend to have a rotten time with their present.

If only the Greeks and the Turks, the Arabs and the Jews, and all sorts of Irish would let go of the past, they and the world would be far better, off.

One cause of American felicity is the nation's indifference to history, its disinclination to brood upon the past. Even the South has at last given up fretting over the War Between the States, and is unquestionably a much happier place as a result.

Nations, like people, tend to remember the wrongs done them and forget about wrongs they inflicted upon others. Happy America, having come unscathed through the centuries, is free of the historical obsessions of the Europeans.

Americans made it up with the Germans and Japanese far more quickly than other nations, and 30 years of hostility towars China is now being washed away with astonishing ease. That hostility was really very superficial.

This is a great American strength, and a lesson to the rest of us. The other side of the coin, forgetting the wrongs one has done, is more difficult to achieve with proper decorum.

White Americans undoubtedly did treat the Indians abominably, and the subject should certainly be taught in schools, but it is a bit extreme to cede half of Maine to their descendants in reparation. On the other hand, the greatest of American sins, slavery, is still being paid for, more than a century after abolition. The people who pay the most, of course, are the slaves' descendants, but the burden on the rest of the country is still immense, an inescapable historical legacy.

In matters foreign, the United States has nothing on its consicence as heavy as the crimes of the Germans or the Runssians -- or the French and British, for that matter.

The French forgave themselves for the First Indochina War rather more hastily than was decent, and for the Algerian War more rapidly still, but since the Vietnamese and Algerians have long since moved on to other things, it cannot really be argued that France is now wrong to consider those episodes closed.

Some time soon, the same thing will apply to the Second Indochina War. The United States will have paid its debts to its defeated friends. Its victorious enemies, if they have any sense, will look to the future instead of replaying the past.

As long as America, or any other country, does not deny its past and its responsibilities, passions will legitimately die down, old men will forget, and finaly even Richard Nixon will be left in peace.