Tall, affable, bespectacled, and just ever-so-faintly rumpled as benefits a man who lives much of his life out of a suitcase, the Most Rev. Robert Alexander Kennedy Runcie is precisely what Agatha Christie has led us to believe an archbishop of Canterbury should look like.

But there were indications during his visit here this week to preside over the convocation of primates from the worldwide Anglican communion, that Runcie is not your conventional churchman. There are signs that the 102nd archbishop of Canterbury is intent on using his high office to try to ease some of the world's political tensions.

In office just over a year, he already has had a significant impact on diplomatic relations between England and the current revolutionary government of Iran; he has been immortalized -- along with Pope John Paul and the president of Ghana -- on an African postage stamp. Next month he will make history when he visits Northern Ireland and joins Roman Catholic Cardinal Tomas O'Faich in public prayer there.

And just this week he announced plans for an unprecedented joint public worship service with Pope John Paul in Canterbury Cathedral when the Roman Catholic leader visits the British Isles next May.

Some of the archibishop's priorities were evident this week when in two public appearances here -- Sunday at the Washington Cathedral and Tuesday at the National Press Club -- he bore down heavily on the peril of a world nuclear holocaust.

"The church must be concerned that the evil of nuclear weapons should be constantly underlined," he told the press club audience. He called for a "religious war on hygienic words which feed complacency and on propaganda and distortions which increase mutual hostility."

A decorated veteran and offer of the Scots Guards in World War II, he acknowledged that "force is sometimes necessary to maintain order" and to indicate a determination "to preserve our liberties." But at the same time, nations "must also search for ways of reducing tension," such as "some attempt to negotiate a ban on tactical nuclear weapons," non-proliferation treaties and "negotiations to limit chemical warfare."

In the question period, the hinted at the role he hopes to play in reducing world political tensions by noting his willingness to help open unofficial channels of communication between national leaders. "Since there is a religious issue involved in so many trouble spots of the world, I believe it is the responsibility of church leaders to try to make contacts," he said.

Even in conflicts involving the officially atheist Soviet Union, he said, "I believe that some of the contacts I have with the Soviet [russian Orthodox] church will help."

The archbishop "has no systematized program as such" for putting political leaders of belligerent nations in touch with one another, said Terry Waite, the prelate's foreign affairs adviser. But he added, "He maintains a large number of contacts and he keeps the lines open."

"He believes that if you can maintain open channels between people, you can sometimes reduce the tension," Waite continued, adding, "he's politically smart enough not to be naive."

Runcie has set himself a schedule of visiting his international church family at the rate of five "major tours" every two years, said Waite. While the archbishop touches all the proper ecclesiastical bases in each place, he makes other contacts as well.

Yesterday, for instance, he break fasted with Robert McNamara and other executives of the World Bank, and later in the day, along with the other primates, paid a call at the White House. "It's a principle with him that when he goes to any country he will meet with the president of that country." Waite said.

And the postage stamp was the result of a photograph of him with Ghana's president and Pope John Paul taken during a tour that coincided with the pope's six-nation African visit last May.

In between church meetings in New York, later this month, he will call on the secretary-general of the United Nations and later meet with several hundred Wall Street investment experts. "He wants to talk with them about how the more technically advanced nations can have a role in aiding the Third World," Waite explained. "He wants to say something about that at a time when aid is being cut back."

Earlier this year, Waite helped carry out the archbishop's most spectacular diplomatic coup thus far, when he went to Iran and negotaited successfully with the revolutionary government there for the release of seven Anglican church leaders -- four Iranians and three Britons -- imprisoned last September.

"By December [of last year] the situation had deteriorated badly" for the seven, who had been accused, on the basis of forged documents, of being spies, Waite said. "The archbishop wrote a private letter to [Ayatollah Ruhollah] Khomeini saying, 'World you allow a member of my staff, on religious and human grounds, to come and talk?'"

After a considerable period of time, and after the request was made public, Khomeini assented. Waite left London on Christmas day, stayed in Iran for a week, during which "I was able to prove the charges were false," and by the end of February "all the Anglicans were pubicly cleared on [Iranian] TV," he said.

The three Britons left the country. The Iranians stayed, but "we phone them up periodically to make sure they are all right," Waite said.

Waite acknowledges that the archbishop "stuck his neck out on Iran. It could easily have gone wrong. But he was accepted by the Iranians because he was a respected religious figure, someone they could trust. What they said to me was, 'We don't trust politicians one inch. We trust religious leaders.'"

Official biographies of Runcie note his hobby as a pig breeder, a venture he got involved in, according to Waite, when a British couturier who had designed some vestments for him invited the archbishop to join him in raising pure-bred pigs. When he visits Iowa later on his American tour, Episcopalisans there will present him with a pure-bred hog and the money to start a pig breeding project in any Third World church project of his choice.

Runcie's pigs have become a standing joke for him and his staff, but the Iowa gift, Waite observes, "makes a lot more sense than another ceremonial cross to gather dust on . . . shelves."

Two qualities Runcie brings to his office are a ready wit and an inclination not to take himself too seriously. He explained to his Press Club audience that, as archbishop of Canterbury, he sits in the House of Lords "on the only bench which has arms, because one of my 18th century predecessors was so consistently drunk that he was in the habit of rolling off the end of his bench onto the floor."

He continually pokes fun at the term "primates" to describe heads of Anglican churches, as "so zoological, as though we should be bracketed in your news columns with the mating of pandas."

And he disarmed the feminists in the audience, who disapproved of his opposition to ordaining women to the Anglican priesthood, with a story about his wife, "a lady of independent life, a professional pianist, who doesn't let me forget" women's concerns.

He said that his wife, who will play a concert in Los Angeles later this month while her husband tends to church matters there, was choosing between a green dress and a red one on a shopping tour. "She finally decided the green one would be better," Runcie recalled, because, she told the clerk, "My husband wears so much purple" -- the color of the shirts Anglican bishops wear with their clerical collars.

To which the clerk, all unaware of the identity of her customer, murmered approvingly: "Oh, trendy husband."

She may have been more perceptive than she knew.