Three bombs exploded in central London early today, injuring four persons, police said. A series of bombings yesterday in five other English cities and near Belfast, Northern Ireland, also were reported by police.

Investigators speculated that the blasts were part of a pre-Christmas terror campaign by the outlawed Irish Republican Army. But they said no group has asserted responsibility.

Police said there were a total of 11 explosions that injured at least 14 persons.

The London bombs went off near the British Museum and in a nearby basement parking area of the YMCA. A 70-year-old security guard on his way to work was hospitalized for shock and three persons in the YMCA were hospitalized for smoke inhalation, according to police.

Near Belfast, a bomb explosion yesterday wrecked the automobile of a prison official as he drove to his job at Maze Prison, where IRA terrorists are held, police said. He was hospitalized but was said not to be in serious condition. Gunmen also fired into the house of another prison official, police reported.

The mostly Roman Catholic IRA has been fighting for nine years to drive the British out of Northern Ireland and merge Protestant-dominated Ulster Province with the overwhelmingly Catholic Irish Republic.

The explosions yesterday in England occurred in Bristol, Coventry, Liverpool, Manchester and Southampton, all about 2 a.m. and all the targets were businesses. No warnings were given.

In the worst of yesterday's explosions, seven persons were injured by flying glass when a bomb exploded behind a showcase of Maggs department store in downtown Bristol, authorities reported.

Two persons were slightly injured by one of two bombs exploding in Liverpool, a port city in northwestern England with a large Irish population. No injuries were reported in four blasts in Manchester, Coventry and Southampton.

Fifty-eight people have been killed and about 1,000 injured by IRA bombs and bullets on the British mainland since 1971. The last attack here came in early 1977, when 13 incendiary devices were planted in London department stores.