The first time C.P. Snow really met Einstein (not counting once or twice socially at events where Einstein bestowed a smiling cordiality on absolutely everybody) he felt that he was being presented to a fairly good-natured Old Testament prophet.

"Isaiah?" someone asked.

"The Second Isaiah," said Snow.

"The beautiful one -- building up the old waste cities and all that," a fellow prodded.

"Exactly. That Isaiah."

"You say a fairly good-natured prophet. Not entirely?"

"No. It is a disservice to Einstein's memory to sentimentalize his good nature. So not entirely."

Lord Snow, raised to the peerage in 1964, is not only an ornament of the House of Lords (to which he commutes by subway from his house in London's plain and costly Belgravia) but also and especially a novelist of international note and writer of revealing sketches about scientists, policians and novelists.

Tonight he delivers the prestigious Frank Nelson Doubleday Lecture at the Museum of History and Technology, a black-tie affair requiring admission card.

"The lecture I have written would take at least two hours to deliver," he said, settling back in the none-too-hospitable arms of a prim Empire sofa in the museum's reception room.

The acting director of the museum, Dr. Otto Mahr, sat on a little chair near Lord Snow and looked quite brave.

"In fact," said Snow, having relished his little shock, "I shall cut it substantially. I shall leave out all that stuff," he said with a lordly gesture to 40 typed pages, "and just talk about Einstein the man.

"I have always said that the worst lecture, that is just spoken, is preferable to the very best lecture that is merely read off the pages."

There is irony here. Possibly few deliverers of prestigious lectures have the art to spellbind. No offense to them, but the art of enchanting people after supper, and of keeping them awake, is excessively rare nowadays, and Snow is one of the few proven masters of it. So much the worse that he, of all lecturers, should be one of the very few who ever thought of abbreviating a remark.

"Of all the men I have met," he went on, "Einstein was of course the greatest thinker, and the one most different from all the others.

"It is true I have met and written a bit about many leading men -- Bohr, Hardy, Lloyd George: I think it interesting you remember the one about Lloyd George best. He was quite an exceptional man. Like a much-improved Franklin D. Roosevelt, if you will not take that amiss.

"Unlike most men of his position, Lloyd George listened well. Someone once put it wickedly: "'The difference between Lloyd George and Winston Churchill was simply this. That if you said the word "balloon," Lloyd George would spend an hour learning everything you knew about ballooning, whereas Winston would take an hour lecturing you on everything he knew about it.'"

"That is a wicked thing to say," his visitor observed.

"Yes," said Snow, not allowing himself a tremendous laugh, but thinking an organic grin involving most of his head might be all right.

"Einstein," he said, "was friendly with all, but no one really knew him. When I say he was more different from other great men than any other individual, I don't just mean that he was, of course, the greatest theoretical physicist since Newton, and no human has ever thought with greater power and clarity about the nature of the universe.

"But I also mean that psychologically -- the makeup of his psychological nature was further removed from us than his conceptions of his physical world.

"To those who knew him best, he seemed more incomprehensible after years of contact than when they first met him.

"Have you got a car?" Snow asked the visitor.

"Well, then, how about a walk?"

Snow, in his conversation as in his art, likes to toss in a few changes of tone, not to say jolts.

"Very fine," he said, peering down Constitution Avenue. He turned into the Mall and inquired what that ecclesiastical-looking thing was over yonder.

"The Smithsonian Institution," he was told.

"Wasn't he English? As I remember, some of his family changed their name (Smithson was illegitimate) and one of them married the heir of the Duke of Northumberland. What is that over there?"

In this way Lord Snow learned everything of consequence about the capital, pausing occasionally to compliment the balmy weather or some prospect, but not for automobiles.

"Lord Snow, some fellow may come wheeling around here awfully fast, and maybe if we walked over there..."

"Yes, indeed," he would say, giving one a great bear-paw swat between the shoulders, as if one had said something diverting beyond measure.

With unperturbed pace, then, he strolled for an hour, mentioning a fine physician who recommended jogging and died in that faith.

"Made no noise about it," said Snow, his eyes following several joggers, "just died jogging. Of course when I was young, I used to play games."

He is only 73, but maybe would not mind if you thought he was born shortly after Stonehenge, and his portly frame and studied, highly amused manner are a slowly walking reproach to the tense electric earnestness of runners.

"You might like my new book on the realist novelists," he said.

"I include Stendhal, Balzac, Dickens, Dostoevski, Galdos, Prou--"

"Galdos?" you may interrupt. "A low philistine, but I never heard of Galdos."

"Never mind," said Snow."Most people haven't. He is a great Spanish novelist. He may well rank with those other great names, though not well known in our language. I must say I included him with a certain, ah, satisfaction.

"I do not know how many bastards he had. It is thought to be a considerable number. You know he had lunch every day with his two sisters, just the three of them, very grim and proper, and at 2 p.m. he arose.

"And where do you think he arose to? To the poorest part of town where he met young girls. I must say that with some of them there was a continuing thing.

"He did this every afternoon until he went blind. Then he went in the mornings, led by his butler. His funeral -- for he was tremendously loved -- was the greatest funeral in many years."

Snow is widely admired for what is called the "revealing anecdote." But more than that, perhaps, he speaks as the historian Gibbon used to write, never stilted, always alert, always easy on the ear and able to convey outrageous information, if need be, without gloating, without alarm, without prudery and without malice. Not more than normal glee.

"Oh, I very much enjoy thinking about doing it -- my work -- but I cannot say I enjoy doing it. Yes, people often comment on my laugh.Once in the Kremlin I was laughing -- Peter the Great's side boots, as I recall -- and a prim young woman said people were looking at me."

Lady Snow (the novelist Pamela Hansford Johnson), he said, recently recovered from an illness, was unable to come with him on this trip, and this brought reflections on the strain of travel and of our century. He spoke easily of other centuries and fine fellows in them, which reminded him:

"I knew a don once who was forever talking of 'the last century.' It took a while before you learned he always meant the 18th."

He said he has many interests, but is not much concerned with gardens, birding, dogs, and yet he has plenty to talk about. He greatly likes pictures and collects contemporary ones in a small way. He has a brother who is a gardener, he said, and who comes to town to fidget with the Snows' garden, though in fact "the roses, well, you can't stop 'em blooming."

He has a son who is a China specialist, and is either on his way to China or his way back -- there is a good bit both ways.

Lord Snow, an aristocrat to end all aristocrats, is a son of a clerk in a local shoe factory in Leicester. Young Snow did well in chemistry, then to Christ's, Cambridge, where he was a physics fellow and later tutor. In World War II he advised the Ministry of Labour on scientists they used, and then became Civil Service commissioner. He was knighted in 1957.

An appealing aspect of his conversation is the steady return to men of grandeur -- with or without their bastards -- after interludes of dead joggers and similar side issues.

"Einstein behaved uncharacteristically in his distaste for Germany," he said."It is surprising a man of his stature treated all Germans as a collectivity, unfit for human intercourse.

"In a lesser man it would be more understandable. It is the one thing hard to understand in him. You know he said he was never aware of any anti-Semitism until he was a young man in Prague. But I find that hard to believe.

"You know how schoolboys are. Not all that delicate, and I am sure they were not in the 1890s. Just consider. There he was, handsome enough, but quite different from the Bavarian louts around him.I have nothing to substantiate this, but my feeling is he rationalized many unpleasant things of this sort in his chilhood and youth, and this may bear on his hatred of Germany.

"Another thing. I know that people like to say Einstein was ignorant of social policy, government and that whole area. But I'm skeptical of those who think themselves experts in such fields. Have we done so well that we can claim great expertise?

"The proof of the pudding, you know, and I cannot see that the experts have all that much to be smug about. There is sometimes an extraordinary sense of self-esteem among such people."

Lord Snow thought once of adjusting his gold necktie against his tan shirt, then seemed to reflect further that it was an unnecessary labor and let it stay as twisted as it liked.

He held a schedule four inches from his eyes and garumphed modestly, and suggested a return to the museum, proceeding directly up the main roadway to the door.

He spoke of languages, said he prattles in a number of them, lit a cigarette which one is almost certain is illegal for him, but there you are, all men have feet of clay.

"I think of Einstein. This warmth and sympathy.

"And this complete remoteness at the same time."

Remoteness is undoubtedly the thing Snow has most trouble with, not knowing it himself.

"Do you think it would be all right if I cut my next appointment short? I could have supper and go to bed."

"Who is the woman?" one would inquire.

"From a newspaper. I imagine she is charming," he said.

"Of course you could cut it short," he was informed, "and you should think whether you need to see her at all."

"Thank you," said Snow, who had been afraid it might seem rude. CAPTION: Picture, C.P. Snow, by Harry Naltchayan -- The Washington Post$