Now you take a good steady cow from London and transport her to America and in no time she will fall apart at the seams, right/What with the miasma of the American lowlands and feed from our poisonous pastures.

Thomas Jefferson used to argue our cows were better than their cows, so there. And Washington himself took to defending the physique of American sheep. For not only cows, of course, but all animals and all men and all plants were supposed to deteriorate when exposed to American air, water, earth, and fall readily in one vast conglabulation of degenerate pathology into irremediable doom.

That is one vision of America, seen by the men of Europe, that attracted, if that is the word, the historian C. Vann Woodward.

Tonight in the Jefferson Lecture, an annual platform for some scholar or other at the Library of Congress, Woodward will not so much defend our cows' honor as review the nonsense of European vision.

"How they used us, in their fantasies and for their purposes," he said.

Yesterday he raced into his hotel, the Hay-Adams, to endure an inquisition by the press. His speech was all written, and don't think it wasn't work:

"Journalists think writing is fun, but getting all the things right is real work."

If you assure Woodward, who is one of America's best-known historians, that you can imagine it would be, he will relax a littl.

He was fresh from a visit with President Carter in the White House, where the president gave him an engraving of Thomas Jefferson who looks proud and distinguished, as befits a man who did so much to dispel all this talk of American miasma.

But, Woodward said, Europe was as madly extravagant to praise of America as in derogation. This magni-paradise. Nothing was too improbable, in the way of natural beauty or American industry, thrift, hospitality, morality, etc., for the Europeans to swallow.

Europeans would land in Boston (to show you the extremes of their madness) and profess to see a combination of Eden, the Round Table and the better passages of the Book of Isaiah.

Woodward, now emeritus professor of history at Yale University, is a country boy from Vanndale, Ark., but in 40 years of increasing reputation and honor has come to look like a sage and wear black over-the-calf socks.

Only his voice, now purged of ya'alls, retains the timbre, the softness and the unarguable rightness of his native rhythm.

Jody Powell, the president's press secretary, told him that it was Woodward's book about the populist, Tom Watson, that led him into politics. And Carter himself has more than once been analyzed by pundits within the context of Southern rural populism.

In his book about Watson, Woodward told the whole story of that celebrated demagogue who came at last to foam against Roman Catholics, Jews and blacks. But who began far otherwise, with a dream of uniting the poor and despised of the South into a force that could achieve all the good things of life.

And - a point that recurs - an insistence that the man's evils were the product, not the cause, of the forces so widely deplored by liberals.

Woodward is not beyond zeroing in on the contribution of the North to the deplorable poverty and gracelessness of the 19th-Century South.

He never says so, but his Jefferson Lecture under sponsorshop of the National Endowment for the Humanities might almost serve (with a few substitutions here and there) as a lecture about the South.

In his books he shows the South as a dream-country full of noble people, and its opposite, and his most obvious point must be that to understand history at all one must set aside the foolish joys of scorn and contempt.

Again and again, as he views the European vision of America, he sees the foreign accounts as a better record of the observer than of the observed.

In New Haven now, he says, his time is his own. His editing of a 12-volume history of America for the Oxford University Press leaves him scant leisure. But freedom to slave as you like is different from being a slave.

When he was a youth, the writings of Thomas Wolfe "grabbed very hard," he said, and writers like Allen Tate, Robert Penn Warren, Cleanth Brooks and so on, resulted in a sort of unveiling of the horizons. Woodward shared in the sense of shackles thrown off and inferiorities overcome.

"All provincial," he said, "but maybe it showed country boys could be taken seriously."

Woodward's blue eyes are sober befitting a historican, and do not twinkle overmuch. He had to be reassured, after he was offered the teaching job at Yale in 1961, that the students up there were not just "dabblers."

Even Yankees, he must have concluded, can be serious and worthwile folks, because he stayed there.

He has never felt estranged from his own country, he said; never felt like an exile harping in Babylon.

He left the South for professional reasons, just as he might have left New Jersey.

He was often quoted, after 1954, by civil rights forces, and he marched at Selma. But he never saw much point in the sort of fight that tends to draw the spotlight to the fighter and no much else.

He says he was wrong - incorrect - in his estimate of Southern white acceptance of civil rights. "Too pessimistic," he said. He had thought there would be far more bitterness and trouble than there was.

Wrong, and he thanks God for it.