Iran responds positively on mediation fronts; Tehran's desire for improved relations with Europe and Whitehall seen behind the release of four Britons

Release of the Four Britons seized on spying charges by the Iranian revolutionary authorities was the fruit of intensive private diplomatic effort by a special envoy of the Archbishop of Canterbury.

Whitehall sources say the Iranians decided to let the three missionaries out of detention and drop spying charges because the government in Tehran is anxious to normalize relations with Britain and other West European countries that have been calling for the release of the missionaries.

All three of the Britons are Anglicans; two are women. They were taken into custody on charges that they had plotted with pro-Shah elements to impede the course of the Islamic revolution. For months they were held without contact with the outside world.

British Foreign Office attempts to communicate with the Britons led nowhere. Contact was established when Terry Waite, Archbishop Robert Runcie's specialist on international affairs, journeyed to Tehran and spoke to the authorities.

On his third visit to the Iranian capital, and after cooling his heels for nearly two weeks, he persuaded the government to relent.

The Britons were moved initially to a government reception center, pending return to London. Meanwhile, the revolutionary authorities set about explaining to their followers why spying charges had been dropped and why people initially said to be enemies of the revolution were completely innocent.

They hoped to convey this impression by arguing that letters, said to incriminate the detainees in espionage, had been forged by an enemy of the Anglican Church in Iran.

Extreme revolutionary elements who continued to press for charges against the missionaries had argued that the Anglican Church in Iran was a "converting" church, owning a lot of property in and near the Iranian capital.

British official sources said the revolutionary authorities had been told by West European governments that normal relationships with Tehran were impossible unless the missionaries and the detained businessman were released.

The more realistic Iranian officials got the message, but then had to convince radical groups of the sense of the argument.

At one point the radicals were said to be demanding the release of two Iranians held on criminal charges in London as a condition of the return of the Britons to their own country.

The Iranians were being held in connection with an alleged attempt to plant a bomb in central London.

Archbishop Runcie's special envoy is a towering, bearded foreign affairs specialist who is personally believed to have played a big part in getting the idea home to the Iranians that further detention of the Britons was futile and self-defeating.

Four Iranian Anglicans, also taken into custody in August, were set free at the same time as the Britons.

The British missionaries were said to be in good spirits and to have no criticism of the conditions in which they had been held. They were said by Mr. Waite to be nervous about the publicity they would receive when they returned home.

In Whitehall their release and pending departure for London was seen as a breakthrough comparable to that achieved in the case of the American hostages. It is felt, however, that it will take months, if not years, to restore relations between Tehran and London to a reasonable footing.