LONDON (AP) _ Britain on Monday announced that a 56-year-old woman would become the next head of its domestic intelligence service - a position that did not officially exist until two years ago.

Stella Rimington, deputy to the current director general of MI5, Sir Patrick Walker, is the first woman to hold the position. Her appointment is effective in February when Walker retires.

Mrs. Rimington, a member of the security services for 22 years, will be responsible for all counterintelligence activities in Britain and Northern Ireland.

''This is no mere civil service appointment,'' said Chapman Pincher, a veteran writer on espionage. The head of MI5 is an administrator who is ultimately responsible for directing counterespionage operations and coordinating with other security organizations like the FBI, he said.

The job pays $140,000 a year.

''My wife's career is her own business but naturally I am delighted for her,'' Mrs. Rimington's husband, John, told Press Association, Britain's national news agency. ''She is a very kind and straight person and the country is fortunate in having her services in such a position.''

The couple has two daughters.

Home Secretary Kenneth Baker announced Mrs. Rimington's appointment Monday in accordance with the 1989 Security Service Act. His news release said no photographs or interviews would be available.

Previously, while the names of heads of MI5 were known, publishing them was a breach of the Official Secrets Act.

In 1989, the Security Service Act acknowledged for the first time the existence of MI5 - originally Military Intelligence Section 5, now officially the British Security Service - and made the service accountable to Parliament.

The act also established a Security Service Commissioner who reports each year to Parliament and a Security Service Complaints Tribunal, which rules on complaints against MI5.

A spokesman for the Home Office, speaking on condition of anonymity, said there were 55 complaints to the tribunal last year. Fifty-two were rejected, one was withdrawn and two are pending.

The Security Service Act does not apply to MI6, Britain's military espionage service.