The scene was as improbable as any other aspect of the bizarre tale of Arkady Shevchenko: the defecting Soviet career diplomat relaxed in a dark suit, was greeting some of the writers, publishers, lawyers and other establishmentarians who haunt New York's grand and exclusive Century Club.

At the time, rumor had it, he was jumping from hideout to hideout in the Pocono Mountains. Sources in the Washington intelligence community said he ought to be squirreled away in the safest of safe houses. But - on Thursday afternoon, at the cocktail hour - Arkady Shevchenko was having drinks in the Century Club with his lawyer, his American publisher and a number of others.

"Don't you feel you're in danger?" someone asked the Russian who is the highest ranking Soviet official ever to defect (if that is what he has done).

"Oh no, I'm fine," he replied.

It was all friendly. Ernest Gross, the former U.S. official who - by his account - was retained out of the blue to represent Shevchenko last week, presided. When one visitor pressed Shevchenko on a specific point, Gross waved it off - "no business," he said.

One of the people Shevchenko talkd with in the Century was Robert Bernstein, president of Random House. A subsidiary of Random House, Alfred Knopf, signed a contract with the Soviet oficial several years ago to write a book.

And that is another improbable aspect of the table. Well-placed sources revealed yesterday that Knopf decided to sign up Shevchenko to write what the publisher presumed would be an official, Soviet-line book on some aspect of international relations, at least partly because the firm wanted to balance its list of books by Soviet dissidents.

No one at Knopf, it was learned, thought that Shevchenko would write anything but approved-in-Moscow prose. Indeed, he had already handed in half a dozen chapters which fit that description.

One curious touch, though: At the time Shevchenko agreed on a contract with Knopf (about three years ago), Soviet regulations required Soviet writers to deal through their government's international copyright agency, or some official publishing agency, Shevchenko did neither; he made his own deal.

Then there is the matter of Ernest Gross, a distinguished lawyer, once assistant secretary of state, three times an American delegate to sessions of the U.N. General Assembly. Gross' story is that the telephone rang last week and it was Shevchenko calling:

"You might be surprised to hear from me, but I have heard of you, I have made some inquiries. I have some difficulties."

In sum, as they used to say to Perry Mason, I need a lawyer.

"Put it in writing," Gross says he replied. So Shevchenko put it in writing.

That was a week ago Thursday. The night before, Shevchenko told Gross, he dined with Oleg Tryanovsky, the Soviet ambassador to the United Nations. Perhaps it was something he ate?

On Friday Shevchenko wrote a lettion not to return to the Soviet Union, and explaining why. Gross won't say what the reasons were.

Gross, by the way, asked the U.S. government to provide security for what basis? At whose instruction? No Shevchenko, which it has done. On answers.

A footnote about Gross: Among his ties to the establishment have been membership and chairmanship of the executive committee of the Free Europe Committee, the body that has overseen Radio Free Europe, until several years ago a Central Intelligence Agency - financed operation. Did Gross have anything to do with the CIA?

"That is an absolute lie," he said emphatically on the telephone yesterday. Yes, he knew about the CIA connection to Radio Free Europe - he always opposed it, he said, and was pleased when it ended.

Only Shevchenko has asked him to represent Shevchenko, Gross said.

According to Gross, Shevchenko asked him to call the State Department and advise officials there that he was arguing with his government and planned to stay on in New York (where he was the highest ranking Soviet in the U.N. Secretariat) against Moscow's wishes. Gross says he made the call.

So Shevchenko decided to risk all - knowing, certainly, that the he might have to ask for political asylum in America - without any direct conversation with any U.S. officials? No rendezvous with men in raincoats? Nothing?

Would John Lee Carre write it like this?