A mysterious telephone call to the Canadian Embassy in Tehran on Jan. 19 by an unidentified man saying he knew that Americans were being provided sanctuary prompted the decision to dramatically smuggle six U.S. diplomats out of Iran Monday.

In his first press conference since masterminding the cloak-and-dagger escape, Canadian Ambassador Kenneth Taylor said today that Iranian officials may have known about his American "house guests" and decided to tolerate their three-month stay in Canadian residences.

But the constant fear of being caught -- underlined by the threatening telephone call -- became so intense by the third week of January. Taylor said, that he began the elaborate preparations to supply the Americans with Canadian passports and airplane tickets to West Germany.

On the climactic day of departure early Monday morning, the Americans were driven to the Tehran airport in a Canadian Embassy car. Wearing clothing and carrying overflowing luggage provided by their Canadian hosts, they had prepared themselves to mask any sign of regional American accents, Taylor said.

"They were the only people to wear two maple leafs," Canada's national emblem, said the diplomat, 45, a relaxed, hushy-haired man who has become a national hero since pulling off what has become known here as the "Canadian Caper."

Final plans to spirit the Americans out of Tehran were made only after he concluded, along with officials in Ottawa and Washington, that the stunning escape would have no "negative impact" on the Americans held hostage in the U.S. Embassy in Tehran.

The six Americans had fled the beseiged U.S. Embassy while Islamic militants were rounding up their colleagues in the front of the 24-acre compound on Nov. 4, Taylor said. For the next several days, he said, the American escapees lived with friends throughout Tehran.

On Nov. 8, Taylor received his first call from one of the Americans. The caller said he and four fellow diplomats had managed to find temporary lodging an uninhabited house but "it was increasingly difficult and they wondered if we could provide a safe haven," he said. They received help from "other rfiendly ambassadors," Taylor said.

After a breif discussion with other Canadian Embassy officials, Taylor decided to send a coded cable to his superiors in Ottawa, recommending that the Americans be given shelter. Word came back from the External Affairs Department in Ottawa "immediately concurring" with his suggestion, he said.

A second call from the Americans came two days later. The diplomats were having even greater trouble finding refuge, and they asked Taylor if "it would be acceptable if we made a rendezvous on that Saturday afternoon [Nov. 10]," he said.

"From that Saturday afternoon on, they remained with us until their departure on Monday," recalled the ambassador.

Another American called Nov. 22, saying he had been staying with friends, but "his position was one which needed security," said Taylor. "He arrived to join us Nov. 22. That made the sixth."

For almost the next three months, the Americans lived in the staff quarters of the official Canadian Embassy in the hilly, affluent section of North Tehran and nearby Canadian residences. They ventured forth only when it was absolutely necessary, Taylor said.

At one point, two of the Americans had to be moved because the Iranian owner had decided to sell the house and wanted to show it to prospective buyers, said Taylor.

The long vigil was described by Taylor as "a weekend vacation that extended for three months." The days "were rahter long" with the Americans staying busy by reading, playing bridge and scrabble and talking, he said.

"The six people were always in remarkably good spirits," he said."You've got probably the six best-read foreign service officers now. I'd nominate any one of them for the world scrabble championship.

"If they saw themselves getting a little depressed, they just looked at their position vis a vis everyone else" in the U.S. Embassy.

Iranian custodial and domestic workers at the Canadian Embassy were told the Americans were "Canadian friends visiting us," Taylor said.

No suspicions were raised by the extra food purchase, he added, because spot shortages were common and embassy official as frequently made large purchases.

Although his embassy staff and guests remained anxious throughout the venture, he said, the first "unsettling" moment came Dec. 10 when he received word that a newspaper disclosure of the Canadian hideaway might be written from Washington. The story, however, was held back.

Several possibilities were discussed for getting the Americans out.

But Taylor finally decided that flying was the "normal way" to leave Iran and would most likely raise least suspicion.

Canadian passports were believed to be the safest exit papers for the Americans, he said, because of the "possible surveillances American passports would create." By the middle of January he had received passports from Ottawa, approved by a special Cabinet order.

In the middle of the month, he began phasing out embassy personnel. Officials leaving Iran by air were instructed to report back on the methods used by Iranian custom officials at the airport, he said.

When the unidentified caller telephoned the Canadian Embassy with his ominous message that he knew of the clandestine mission, Taylor said, he knew that the Americans had to be removed from the country quickly.

The call was placed in the middle of the day while Taylor was out of the embassy. His wife, Patricia Taylor, answered the phone and heard a man with an indistinguishable accent say he was aware that Americans were being sheltered within the Canadian residences.

The caller first insisted on speaking to the ambassador. Told that Taylor was not in, he demanded unsuccessfully to speak of two of the Americans inside -- Joseph D. Stafford, a consular officer, and his wife Kathleen, a consular assistant.

Meanwhile, Prime Minister Joe Clark told a press conference here today that he understands there have been "promising" discussions about the hostages at the U.S. Embassy in Tehran.

Clark said he had been told the discussions about the hostages involved "at least" the United States and Iran, but told reporters he could not go into detail. He said Canada was not involved.