LONDON (AP) _ The government today said it will deport nine more Iranians, including two former employees of Iran's Embassy in London, unless they leave voluntarily within five days.

Another group of nine Iranians, all former embassy employees, were given 10 days to get out and had to leave Britain by Sunday or be expelled. One of them failed to leave and police arrested him today, the Home Office said.

Foreign Secretary Sir Geoffrey Howe told Parliament two weeks ago that Britain planned to expel an unspecified number of Iranians following Ayatollah Ruhollah Khomeini's Feb. 14 death sentence on British author Salman Rushdie.

''We perceive these individuals to be a security threat,'' said a Home Office spokesman, requesting anonymity.

The nine ordered out today have until Monday to leave.

About 25,000 Iranians live in Britain, including 2,400 students.

Iran broke diplomatic relations March 7 after Britain refused to ban Rushdie's novel ''The Satanic Verses,'' which Moslem religious authorities say blasphemes Islam.