Strife over Northern Ireland took another violent turn Monday: * In the fifth bomb attack by Irish Republican Army guerrillas in London in two months, a toy gun packed with explosives blew up outside an Army barracks. Two women were injured in the blast, which Scotland Yard said might be part of a series of IRA pre-Christmas bombings that has killed three people and injured over 20.
* Militant Protestants in Belfast called for a strike to paralyze Northern Ireland. The fiery Rev. Ian Paisley challenged British rule by calling for a parade of his armed vigilantes to back his demands for a crackdown on the IRA.
Police and troops were placed on alert to prevent trouble at the demonstrations - and especially to guard against guerrillas launching provocative attacks on Mr. Paisley's ''Day of Action.''