The Iranian Embassy indicated it would help in the search for foreign hostages in Lebanon if Britain continues efforts to find four Iranians believed held in Lebanon.

British diplomat David Reddaway arrived in Tehran Friday for talks about the hostages. It is Britain's first diplomatic visit to Iran in a year.Those developments, along with meetings in London between an Iranian envoy and Archbishop of Canterbury Robert Runcie, raised new hopes for the release of the three Britons held hostage in Lebanon.

"I think it is bound to help," Reddaway, a senior official at the British Foreign Ministry, said of his Tehran visit. Speaking before leaving from Heathrow Airport, he said that while in Iran he planned to assess the possibility of Britain resuming diplomatic ties.

Britain withdrew its diplomats from Iran a year ago after one was beaten up in apparent reprisal for the arrest of an Iranian envoy in England on shoplifting charges.

Neither the Iranian Embassy nor Runcie, who left for a three-week vacation in Philadelphia, would comment on Runcie's Wednesday night talks with Mohamed Reza Said Mohamedi, an Iranian Foreign Ministry official.

Runcie is the spiritual head of the Church of England. Church envoy Terry Waite is among the three British hostages.

An Anglican bishop went to Lebanon last month to initiate inquiries about the fate of four Iranians believed kidnapped by Christians.

A statement from the Iranian Embassy, released Thursday night, said:

"1. Any attempt in locating the Iranian hostages in Lebanon would be appreciated by the entire people of Iran.

"2. We are sincerely exploring the possibilities and ways of mutual assistance in tracing non-Iranian hostages in Lebanon.

"3. We fully share the views expressed by the archbishop of Canterbury and appreciate his initiatives in solving this problem."

Pro-Iranian extremists are believed to hold 18 foreigners, including nine Americans, hostage in Lebanon. The Hezbollah faction, over which the Iranian government wields considerable influence, is believed to be the umbrella organization for groups holding the hostages.

Waite disappeared in Lebanon in January 1987 while trying to secure the release of hostages.

The other Britons missing are television journalist John McCarthy, who was kidnapped April 17, 1986, and teacher Brian Keenan from Northern Ireland, who has been missing since April 11, 1986. Keenan holds British and Irish nationality.

The hostage held longest is Terry Anderson, chief Middle East corres-pondent of The Associated Press. He was kidnapped March 16,1985.