LONDON, OCT. 12 -- A terrorist bomb exploded in a London pub at lunchtime today, injuring at least seven people in what police called the latest of a series of Irish Republican Army bombings and telephone threats designed to disrupt the city.

Authorites described the bomb as small and said it had been left in the men's room of the Sussex pub, near Covent Garden in London's theater district. One middle-aged man suffered serious head injuries and underwent emergency surgery at a nearby hospital, police said, while six other people required medical attention.

The blast was seen as part of a new IRA campaign of small bombings in central London intended more to terrorize and unsettle than to kill. For more than two decades, the IRA has waged a bloody war to end British rule in Northern Ireland.

Since last Wednesday, the IRA has detonated eight bombs in London, most of them in trash cans and telephone booths, injuring at least 14 people, the majority hit by flying glass. Most of the blasts have been preceded by telephoned warnings.

After an explosion Sunday in a phone booth outside Paddington Green police station, where terrorist suspects routinely are held and interrogated, the IRA issued a statement in Dublin that warned: "British military and political leaders should take this signal of our intentions seriously."

Today's bombing appeared to represent an escalation of the violence. The pub is in one of London's busiest districts, routinely thronged with tourists and lunchtime crowds. A caller who warned a radio station just minutes earlier gave only a vague indication of where and when the bomb would go off, as opposed to the specific warnings received in previous incidents.

The IRA also has issued bomb threats against the London subway system. One of them two months ago forced authorities to shut down at least six stations at the height of the evening rush hour, stranding a million commuters.

The blast at the Sussex pub today also disrupted the city's normal traffic flow. Police, worried that a second device might have been planted, cordoned off a half-mile radius, and London streets quickly succumbed to gridlock.

Authorities viewed the bombings and threats as a psychological campaign and urged Londoners not to give in. "Whatever you do, do not be deterred from going about your normal business," said Cmdr. George Churchill-Coleman of the police anti-terrorist branch. "This is going to happen from time to time."

Earlier this year, the IRA's strategy was to set off more powerful bombs, but less frequently. In February, a bomb at London's busiest train station injured 29 people. In April, massive blasts damaged a busy suburban interchange and destroyed a building in London's financial district, killing three people and injuring scores. But such attacks require large amounts of explosives and careful planning. Over the summer, police raids turned up a large amount of IRA explosives, dealing what authorities called a telling blow against the group's London-based operatives.