IN HIS 10 YEARS with the CIA, Charles McCarry will tell you, there were two kinds of men that he never met: "One was an assassin and the other a Republican."

But he did know many versions of Paul Christopher, the covert agent who moves under deep cover through McCarry's espionage novels, which became a trilogy with the appearance of "The Secret Lovers" a few weeks ago.

Those of the McCarry cult use such terms as "early Eric Ambler" and "the American Le Carre." The nearer truth is that he is mature McCarry. Under cover of a spy thriller, a serious novelist is writing about what he knows - espionage - as a metaphor to comment on Americans of his generation, living in a time that has tested American values and beliefs, both in public and private lives.

"It's difficult to explain without sounding like a pompous ass," McCarry says. "What I thought is that I could use the framework of the thriller in much the same way that Dickens used the format of the Victorian novel of melodrama to comment on the social issues of his day.

"Christopher's life is the life of 20th-century Americans, at least a certain class. It (the trilogy) moves from the innocence of 'The Miernik Dossier' to the cold professionalism of 'The Secret Lovers' through the destructive - no, cruel - idealism of 'The Tears of Autumn.'"

McCarry may write espionage thrillers. But they are not escape literature.

I'm convinced that there is no more intelligent or unemotional group of men on earth than ourselves. That, if I may say so, is our principal weakness. Because our people are so bright, because our resources are so huge, we consistently tinker with reality . . . We have come to look on our work, in the field at least, largely as a sport. - Statement by Paul Christopher, American intelligence agent, in "The Miernik Dossier."

McCarry agrees with his fictional hero:

"The men that I worked with in the agency were the most honorable and ethical in personal relationships of any men with whom I have ever worked."

McCarry is a former small-town newspaperman, one-time speechwriter for Eisenhower Labor Secretary James Mitchell and Republican Vice Presidential candidate Henry Cabot Lodge in 1960, former deep-cover operative for the CIA, magazine writer of profiles of film stars, politicans and Kentucky Derby horses, and now novelist.

He had motored to Washington from his home in Northampton, Mass., and was sipping tea at the dining-room table in a friend's apartment. Rod MacLeish, television commentator and columnist, also has tried a hand at thrillers with "The Man Who Wasn't There." The book plotters sometimes are joined by another friend, Richard Condon, author of "Winter Kills."

McCarry was going to be 47 in a few days. He is Paul Christopher - 10 years later, 10 pounds heavier, an inch or two shorter, perhaps not as tough, certainly with more play of humor; a solid, stocky man with a roundish, open face; medium height, medium brown, medium age. Nothing that quickly distinguishes on first appearance - an asset for any spy.

The fictional Paul Christopher, who gave up writing poetry, probably will never leave the agency. McCarry did in 1967, to write novels.

It was six years before "The Miernik Dossier" appeared in print. Then came "The Tears of Autumn," a stunningly credible scenario for the assassination of President Kennedy, which became a hardback best-seller in England and France and has sold more than a half-million paperback copies in the United States.

McCarry still is trying to convince people that it isn't a true story.

His talent, the gift of the operative, was to separate from years of talk the one phrase that betrayed the truth, and from miles of action the single deed that revealed the person. - Said of Paul Christopher in "The Secret Lovers"

The gift of the operative - for the telling, betraying detail - also is the gift of the novelist.

In "The Secret Lovers," McCarry has written a rich-textured, multi-layered novel - a tale of an espionage coup to smuggle a manuscript out of the Soviet Union; the love story of Paul and Cathy, who wants a perfect union with a man and can't accept Paul's secret life apart from her; a study of men and women who consciously chose to be professional spies, often at fearful cost to their personal lives.

McCarry can sear the memory with spare sentences and the taut phrasing of an intelligence report. Paul and Cahty use "love" as a code word to signal his return to Rome on the 1 a.m. plane. Then comes a cry of loneliness from Cathy in Spain and Paul wants to send her a note of assurance but:

"Because they had made it into a code, he couldn't use the word 'love' in a telegram."

Christopher saw the truth at dawn on the tenth day after the death of Kennedy . . . He knews who had arranged the death of the President. - "The Tears of Autumn"

McCarry was with the CIA when Kennedy was assassinated. He was on assignment in the Congo when he got the news (just as Christopher does in "Tears") from a Belgian priest listening to a transistor radio in an airport.

After weeks in the Congo, he had come back to Rome, tired and with a bad stomach ("as people do who spend six weeks in the Congo"). He and his wife, Nancy, decided to go to their favorite retreat in Siena. There - again as Christopher does in "Tears" - McCarry was awakened on a cold dawn and, looking out the hotel window, saw two Italian farmers in black hurrying to the edge of a woods.

"The idea clicked in my mind," McCarry recalls. "What I did was write a scenario for a perfect operation where everything goes right. Truth in art and life is not the same . . . 'Tears' is entirely a work of imagination.

"Unlike Paul, when the idea clicked, I didn't take off and solve the murder."

Neither did McCarry take off and write. He waited until seven years after he left the CIA to publish "Tears" and then only after the Pentagon Papers had detailed American involvement in the overthrow of Vietnamese President Ngo Dinh Diem.

McCarry's "perfect operation" in fiction is so simple, so fascinatingly logical: The Vietnamese troc (family) of Ngo answered insult for insult, blood for blood, for the death of Diem by arranging, through a Cuban-Russian connection, to recruit an unstable Oswald to pull the actual trigger to kill the American President.

In real life, McCarry wrote a novel. In fiction, Christopher seeks out the truth on a journey that takes him to the back alleys of Saigon, Paris, Rome, Zurich (where a dwarf shimmies down a chimney for information on a Swiss numbered bank account), a hotel room in Washington for a meeting with a White House aide. (Dennis Foley, whose mannerisms change from JFK to LBJ, is not one person, McCarry insists. "He's every special presidential assistant that I have known.")

Throughout the Christopher trilogy, there is a sense of place and atmosphere, the sights, smells and sounds. Like his fictional hero, McCarry lived in Rome (also Geneva and the south of France - "not hardship posts") while working as a covert agent in Africa and Asia. He never operated in the country in which he lived. He was a singleton, traveling on an ordinary passport, never attached to an embassy or consulate.

Christopher went everywhere in the world, looking for men who were capable of acting, and making it possible for them to act. - "The Secret Lovers"

McCarry worked for the CIA from 1958 to 1967. He never was behind a headquarters desk. Every hour of his 10 years with the CIA was spent in the field, working with agents, mostly in Asia and Africa. He never handled a gun or weapon (he knew only one intelligence officer who had a gun; the others regarded him as a "nut"). He never killed a man.

In the espionage novels, Paul Christopher never has pulled a trigger but he has known men were going to die and did nothing. McCarry, as a CIA operative, also knew people who sometimes were in terrible danger.

"Paul is tougher than I am. If I had known an agent would lose his life, I would have warned him - or like to believe that I would have," says McCarry.

Intelligence officers like McCarry work with agents. Agents do sometimes get killed. But intelligence officers don't kill each other ("It just isn't done"), McCarry says. It's better to known the opposition and watch its operation.

Neither McCarry nor Christopher are the burned-out agent of Le Carre's "The Spy Who Came In From the Cold." Nor are they the untroubled James Bond swashbuckler.They come over as decent, honest men who made hard decisions that had to be made. Both have a passion of belief.

"God, this sounds archaic, corny - America, the idea of freedom," says McCarry. "I believe that countries with some freedom work better than countries without freedom. I think it was worthwhile to prevent the loss of freedom. That was what my work - and Christopher's - was about.

"Ghana became independent in 1952. In the next three years - less time than it took Stanley to find Livingston - 32 countries became free. It was evident that, for many the first election was going to be the last."

McCarry did what Christopher does as an intelligence officer. He sought out people capable of acting and gave them money and advice to shore up the democratic opposition - free press, political parties, trade - to moderate authoritarian leaders. He says that he never asked anyone to do anything that was directly and solely in the interests of the United States and incompatible with the interests of the other country.

"Granted," he adds, "that, it was as we saw those interests to be."

Christopher, whose work was a game, hated games. - "The Secret Lovers."

In the late 1950s, McCarry recalls there was a strong, element of prankstering in the CIA. There were all these bright, spirited young men.

"It was almost like fraternity pranks against the Russians - confound them, confuse them. We were better than they were. The CIA is - or was - the best intelligence service in the world."

Now McCarry isn't too sure. He doesn't know how the CIA can operate as an intelligence service, with names of agents printed in newspapers and absolute trust compromised. Satellites and arcane devices may take revealing photographs and overhear conversations. But "you can't photograph political intentions."

"The only way," says ex-operative McCarry, "is to have someone in another government who trust you and tells."

Their friendships were deeper than marriage. They needed each other's trust as other men need love. - "The Tears of Autumn"

There are many sexual metaphors in the espionage trade, McCarry observes. Recruitment, for example, is a "Seduction." Charles McCarry never fantasized about being a spy. From the age of 14, he wanted only to be novelist.

He was accepted at Harvard but decided not to go to college (Paul Christopher did attend Harvard).Instead, McCarry enlisted in the army in 1958 and the next three years were spent on the staff of the army newspaper Stars and Stripes.

His life has turned on a series of "accidents."

One came when he attended the wedding of an Army buddy in Ohio, ran out of money, and looked for a job. The state employment agency said his Army career prepared him for a job on the Elizabeth (Ohio) newspaper. While covering the court house, he met his wife, Nancy, who worked there.

Then came another accident - another Army buddy was writing speeches for James Mitchell. Labor Secretary in President Eisenhower's Cabinet. McCarry joined him in Washington.

Then, with the sale of seven or eight of the short stories that he wrote at night, McCarry and Nancy decided to go to Europe. Mitchell didn't want his bright young speechwriter to leave the government and called Allen Dulles, then head of the CIA.

"I received this phone call," McCarry recalls. "A voice said: 'Hello. This is Mr. D. Your friend knows another Mr. D. and has talked to him.' It took me a while to figure it out and then I blurted: 'Oh, Mr. Dulles.' There was a garumph and then silence on the other end of the line."

McCarry and Dulles' emissary arranged to meet at 10 a.m. the next morning in room 504W at the Statler Hotel (McCarry has nearly total recall; he remembers 30-year-old phone numbers; he never carried an address book - "It may sound melodramatic but people's lives were in your hands.")

A few minutes before 10 o'clock, the 27-year-old speechwriter was waiting in the hallway of the Statler. Ten minutes late for the appointment, a bald man, with "drops of sweat atop his head" and bristling mustaches, came down the corridor. He fitted a key into 502W, tried to turn it, twisted, and damned the door. McCarry finally was emboldened to point out that the key didn't work because it was the wrong door.

"It wasn't the last time, by any means," McCarry comments, "that the CIA displayed its human fallibility to me."

And then comes a laugh, rumbling up from the depths - a betraying mannerism.

McCarry was recruited - seduced - by the CIA and signed an oath of secrecy. Mr. D. impressed the importance of the oath, "probably thinking particularly about getting the key in the wrong door."

McCarry still takes the bond of secrecy very seriously. He says he never talks about any actual operation from his experience as a CIA covert agent. Finally, after his first two espionage novels were published and interviewers kept asking questions about his background, he called the CIA and said he was going to mention that he had been with the CIA from 1958 to 1967 - "full-stop."

"I thought Mac was in Majorca writing the great American novel. Later, in Geneva, I thought he was with the International Labor Organization. And he was doing these free-lance magazine articles."

Joe Judge, senior assistant editor in charge of text for the National Geographic, met McCarry in Barracks T-421 at Camp Pickett in November 1951. McCarry, back from army duty in Germany, was about to be discharged.

"He threw a stack of poetry on my bunk," Judge remembers. "I drew a diagonal blue pencil line through every page. We've been friends ever since."

Judge was the former Army buddy who brought McCarry to Washington to write speeches for James Mitchell. Then, when he thought Mac was writing that novel in Majorca, Judge couldn't let an old friend "starve on the beaches" and suggested McCarry as a speechwriter for Henry Cabot Lodge, who was running as Republican vice presidential candidate in 1960. McCarry then went back to Europe.

"The last time that I saw Mac and Nancy in Rome." Judge recalls, "he said he was tired and coming back to the United States and the Berkshires. He did this lovely piece for us on returning to the Berkshires. I never knew about the CIA until I read the 'Miernik Dossier.' Then I asked if there was any CIA connection and told Mac we couldn't use any more free-lance articles unless it was over. He said it was."

And it was by then - after 1967, when McCarry had resigned from the agency and gone back to the Berkshires.

I doubt if you can understand. I doubt if anyone can who hasn't lived the life . . . I love secrets, we all do. While we're working, we're together in a region of experience where very few humans have ever gone. - Paul Christopher in "The Secret Lovers"

Charles McCarry says he wants to write about the life of an espionage officer as it is - or nearly is. No gimmicks, no trick guns. But men and women who must guard against betraying habits and mannerisms like having a favorite restaurant or taking one puff on a cigarette and throwing it away.

He has no quarrel with mass-audience spymasters who offer pleasure and entertainment. Le Carre does write about the realities of espionage life but he deals mostly with headquarters men at their desks and not the operatives in the field.

McCarry does write about espionage "tradecraft" - safe houses, the "flutter" (the lie detector test administered as an annual rite of brotherhood), code signals like hands clasped behind the back, the meetings in the open to escape bugged conversations (agents visit more zoos, aviaries and parks than most people),' the thumbprint receipt for money.

If there is absolute trust between intelligence officers and their is absolute trust," McCarry replies.

Without a karate punch every other page and gimmickry, McCarry's espionage novels are attracting a growing audience. There is, of course, the hardcore cult of admirers who have "discovered" McCarry.

His first spy novel, "The Miernik Dossier," sold about 16,000 copies in an E. P. Dutton hardback, quite respectable for a first novel (McCarry remembers such figures). "The Tears of Autumn," the second to be published although the action occurs in time after "The Secret Lovers," sold around 30,000 hardbacks in the United States and was a best-seller in England and France. Its paperback edition (Fawcett) has sold more than half a million copies. Dutton has a first-printing run of 25,000 for the "Lovers." It has been bought for six figures by Fawcett for a paperback edition and is a Book-of-the-Month Club alternate.

And Hollywood now has discovered the McCarry espionage novels and is making "background music" for "The Secret Lovers."

"They talked about 'Tears,' "McCarry says. "But it scared hell out of everyone. They were afraid it was true."

Some of them [the English-speaking journalists], hanging together in an atmosphere of sad gossip, knew Christopher in his own name as the correspondent of a great American magazine. Christopher avoided them when he could, and when he could not, he bought them drinks with his own money. It was against regulations to spend secret funds on the American press. - "The Secret Lovers"

McCarry was a free-lance feature writer for the old Saturday Evening Post while working for the CIA. He wrote profiles of Michael Caine, the screen spy, and Laurence Olivier and a feature on the Pieta when it was coming to New York for the World's Fair.

He did this while on compensatory leave from his CIA job ("I must have 4 million hours to my credit"). He says that he never used journalism as cover in the way as Paul Christopher does in the novels.

"I gave Paul the cover as a journalist because it seemed a safe fictional device. When I wrote - and I still believe it - agents did not use journalism as a cover. There may have been a fake press agency with a press card to use in the Congo. But it was my understanding that an agent never used journalism as a cover."

McCarry never did political stories in his free-lance career while in the CIA. As a journalist, he never told anyone he was an intelligence operative - not even Michael Caine, interviewed as a film star whose speciality was spies.

Later, after he left the agency in 1967, McCarry did articles for Esquire, True, McCalls and the National Geographic. He profiled Sen. William Fulbright and Congressman Mendel Rivers for Esquire and did a 100th anniversary piece on the Kentucky Derby for the National Geographic.

"I have this disease - everyone is interesting to me," McCarry says. "I tend to like people whom I write about. I never set out to be hurtful but sometimes facts are hurtful. It is a fact that Fulbright never had voted for a civil rights bill."

He wrote "Citizen Nader," a biography of the consumer activist that some critics took as unneccessarily hard on Nader.

"I never approached a subject with greater sympathy and left with less. I agree with Nader on many things that need opposition . . . But Ralph doesn't seem to be able to oppose a man's ideas without attacking his character. I may be wrong and I think Ralph thinks that I am wrong."

Paul Christopher had been loved by two women who could not understand why he stopped writing poetry. - The first sentence of "The Tears of Autumn."

McCarry begins with the first and the last line of a novel.

"Sometimes I don't know what is going to happen. The characters take on a life of their own and take control. In 'Tears,' I had trouble with Paul. I wanted him to go to the Congo and he kept wanting to get into bed with Molly."

McCarry wrote "Tears" in 55 days. He wrote "The Secret Lovers" in 59 days, up at 6 a.m. and writing 2,000 words a day, later pared by 500 in editing. But these were characters and scenes that had marinated in his mind for a decade or more before they gushed forth.

McCarry grew up in Plainfield, Mass. (population of 110) and went to a one-room school. The teacher gave him the key to the attached library and he devoured its books.

"It was very cold in winter. I put on coat, mittens, and cap. I still can see my breath blowing between me and the book."

By the age of 25, McCarry had writen three novels, still unpublished. He then decided he could write gusto well but that he didn't know enough about of life - a self-detached evaluation that one wishes more young novelists might make.

"I did everything - apart from my being married to Nancy for 25 years - with the idea of gethering material for novels. It sounds cold-blooded but I always thought of myself as a novelist," McCarry says.

He tried speech-writing and then went into the CIA to "learn about human nature," he says and smiles. At the end of 10 years, he had learned so much that "the last thing that I wanted to do was describe human nature." It took him another five years to think about writing, his first espionage novel, "The Miernik Dossier," not a wholly successful attempt to use the framework of intelligence reports, transcripts of conversations, and other documents.

The idea came from an "intellectual conceit" that the young writer had when he was 20 years old: "It was police dossier on St. Paul, a dangerous revolutionary in his time, being surveilled and detailed by the Roman secret police."

Subliminally St. Paul became Paul, whose last name came from No. 13 Christopher Street, where McCarry once lived in New York City.

You're losing your humor, Paul. I've seen it happen to others who stayed in the field too long, do too much . . . Professional fatigue. I believe, in the case of Christians, it's called religious melancholy. Do you play with the thought of getting out? I know you like to be with this girl Molly. - David Patchen to Paul Christopher in "The Tears of Autumn."

McCarry left the CIA in 1967 after a life of 10 years as an agent under deep cover.

At 37, it was time to write if he really wanted to be a novelist. And then he was tired; professional fatigue had set in.

"My wife was very strong and loving. I was away for six to eight weeks at a time. I missed her and she missed me. I had four sons, two born abroad and the other two taken abroad before they could speak English. I wanted to be with my wife and children more," McCarry explains.

And then there was disagreement with the Vietnam policy. In the early days, McCarry points out, you could walk down any main street in the United States and people would have told you that it was stupid to get involved in a land war in Asia. But there was a "contagion of consensus" at one time and a policy that fed on itself. Better for everybody to have given it away in 1960.

"We have suffered. But, God, how the Vietnamese have suffered - and are suffering," says McCarry.

So long as he was awake, he was able to control what he remembered. When he slept, he dreamt of murder. In his dream, he felt fear for himself and pity for Horst Bulow . . . On the street in Berlin, Christopher had felt nothing as he watched Bulow die. - "The Secret Lovers"

The relationship of an intelligence officer to his agent, says Christopher, is based on absolute trust and can run deeper than marriage.

McCarry remembers one of his agents in Africa who he believed had been killed.

"Then, five years after I left the agency, I was riding an airport bus into London. This tall black man in business suit got on. I said 'Peter' (it wasn't his name) and he said 'Charles' and we fell into each other's arms. The other passengers looked at this crazy American and tall black man embracing each other and sobbing."

McCarry does not expect to write another novel about Christopher for a while. He feels that has said all he wants to say about espionage for the time being.

But he has the first and the last line of his new novel.

"The rest is well underway in my head," he adds. "It will be set in Washington and deal with Presidential politics, with elements of the interplay between the White House and intelligence agencies."

McCarry resigned from the CIA for a period while he was writing speeches for Henry Cabot Lodge in 1960. Lodge, he says, insisted on the absolute truth in his campaign speeches and was an earthy man, "180 degrees different from his public image." McCarry, a natural Democrat by his views, could not accept the fact that then "40 per cent of the Democrats were elected as Dixiecrats on an appeal to racial hatred."

"I think these were worthwhile adventures. In retrospect, they didn't work out too well - we didn't liberalize the Republican party and we didn't save Asia and Africa. Maybe that is why I write novels - I can make it come out all right."

It is said without bitterness or disillusionment. And for that matter, it doesn't always come out right in McCarry's novels.