Among all the disagreeable aspects of the U.S. hostage affair in Iran, there was one grand exception: the daring rescue of six Americans by the Canadian ambassador in Tehran and his staff.

The story, as told with the help of a colleague, by Jean Pelletier, the 31-year-old French Canadian reporter who broke it, is a humdinger of a suspense yarn. It also is a good illustration of what the responsible free press is all about.

First, about the yarn. The six who slipped out of the American compound the day the Iranian militant students came over the wall tried various hiding places and eventually sought help from the Canadians. Ambassador Ken Taylor and the Canadian Embassy's immigration chief, John Sheardown, took in the "house guests," hid them in their homes for 11 weeks, and eventually engineered their escape from the country, with the gutsy approval of Foreign Minister Flora MacDonald and Prime Minister Joseph Clark in Ottawa.

Slipping them out of the country was even more dangerous than concealing them there. Plans to have them picked up by helicopter or by a tanker offshore were junked in favor of disguising them as visiting Canadian business representatives and booking them on a regular flight from the Tehran airport. The U.S. Central Intelligence Agency, skilled at such things, helped out by supplying forged Iranian passports, visas, social security cards, drivers' licenses and the rest of what a traveler carries in his wallet. One boner by the CIA could have been fatal, but it was caught in time for a correction when a sharp-eyed Canadian diplomat noticed that one of the fake entry visas had one of the "businessmen" entering Iran the following month.

Exposure at any point before the Americans were safely in the air would have set the Iranian mobs on the run after any Canadians who might have helped harbor the "spies." Taylor already had quietly trimmed the size of the embassy staff. Now he shredded his papers, closed the embassy, and left with his few remaining officers.

Several times the secret almost leaked out. Flora MacDonald herself almost spilled the beans. Pierre Trudeau, then the opposition leader, had been let in on the secret, but in a parliamentary question period he nonetheless accused Clark's government of a "stand-offish" attitude in the Iranian crisis while the United States faced such trouble. Furious, she retorted that such grandstanding involved the lives of the American hostages. She added, indiscreetly, that it involved as well "the lives of Canadians who are in Iran." But the Ottawa press gallery missed the implication.

At another point, one of Taylor's cablegrams, mentioning his "guests," somehow got into a printed diplomatic summary that goes to all senior Exterior Affairs bureaucrats. But if they were puzzled by the reference, no one leaked the story.

It was not a leak but simply journalistic enterprise that enabled Jean Pelletier, Washington bureau chief of La Presse, a French-language daily in Montreal, to become the first reporter to learn that six Americans not accounted for were being hidden by Ambassador Taylor and his staff.

Like many other Washington reporters, Pelletier wondered why U.S. officials were vague as to how many hostages had been taken when the embassy was overrun. He is a bit vague himself as to exactly how he got the story. But, without revealing his sources, he tells of a hunch that became an obsession that eventually was developed into a hard news story by persistent and repeated questioning of officials who might know the facts and be persuaded to give him a bit at a time.

Someone is always telling a reporter to be responsible, and once Pelletier had gotten onto this story, U.S. and Canadian officials ran true to form. So did his editors, gung-ho to get the story into print and fearful that some big paper like The New York Times or The Washington Post would get it first.

Often "responsible" can be translated as laying off a story that will be embarrassing or cause a flap. Those are the easy ones, and a good reporter goes ahead and writes it and a good newspaper goes ahead and publishes it. The hard ones are those like the preparations for the Bay of Pigs invasion, where a reporter cannot be sure whether a vital secret actually is involved.

The story of the six house guests was at the other end of the scale -- an easy call because publication would so clearly endanger human lives. It is to Pelletier's credit that he insisted on sitting on the story until the six Americans were out of Iran. Most other reporters would have done the same.

In fact, at least one other reporter may have done exactly the same thing. A week before the six Americans finally escaped, the telephone rang at Ambassador Taylor's residence and an English-speaking voice asked to speak with Joe or Kathy Stafford, two of the fugitives. Taylor's wife, Pat, stalled, asking if it was a joke and wanting to know who was speaking.

"Look, I know that the Staffords are there; they're staying with you," said the caller. "Can you put one of them on the phone, please."

She said she knew of no one by that name and referred the inquiry to the ambassador. That was the last they heard of the mysterious caller. They don't yet know who he was, but he was using an old reporter's trick.

It is to Pelletier's credit, too, that, once the six Americans were safely out, he went ahead with the story, despite official requests that he continue to sit on it. The immediate danger was over; only the threat of a possible flap remained.

Responsibility for a news reporter and for a news organization means knowing when not to publish but also when a story must be published regardless of pleas and pressures.