LONDON (AP) _ Irish Republican Army bombs that have killed dozens and wounded hundreds in England have not budged the British from Northern Ireland. But one big blast in London struck at the nation's financial heart by scaring insurers away from the city.

Starting in January owners of the glass towers where London wheels and deals may have to absorb the entire loss if IRA bombers hit their property.

The threat of more bombs and no insurance has stirred fears of unrelenting attacks that could bankrupt companies, prompt others to leave London and discourage away foreign investment.

''It's a financial threat of the first order,'' said Bernard Harty, who handles finance for the Corporation of London, the major landowner in the financial district.

''We have five billion pounds ($7.75 billion) of insurable assets. If we haven't got cover against acts of terrorism, the financial implications are quite significant.''

A massive explosion April 10 killed three people, injured 91 and left the 23-story Commercial Union tower a shattered wreck.

When the tower is rebuilt next year, there may be no insurance coverage against future bombings.

The same holds true for large buildings throughout England. The damage from the April blast proved so expensive - estimated by the insurance industry at $1.24 billion - that Britain's insurers decided to cut off terrorist coverage for large commercial customers.

Insurers say the British government should pay for repairing bomb damage. As the insurers see it, the attacks are a poisonous fruit of violence in Northern Ireland, where the government has already footed the bill for $1.05 billion of damage in 23 years of political and sectarian violence.

The government, so far unwilling to cover what could be billions in liability, compares the bombings to unpredictable natural disasters. Trade Secretary Michael Heseltine has urged insurers to find a free-market solution.

Most IRA bombings involve limited property damage, and perhaps a few hours of rail and road traffic disruption. Britons seem determined to defy the bombers, and the violence has not produced any significant political pressure on the government to abandon Northern Ireland.

But the legacy of the financial district bomb may endure long after the damage is repaired, posing a threat to a business center that is the world's No. 1 currency exchange and brings billions into Britain's economy.

Commercial Union Assurance Co. PLC sees both sides of the dilemma. Every floor of its building was destroyed in the April blast.

Similar explosions elsewhere could break Commercial Union if it continues providing terrorist coverage for large corporate clients, said spokesman Ray Morley.

But could Commercial Union itself afford a repeat bombing in its soon-to- be-uninsured building?

''I don't know, but some people won't be able to,'' Morley said Thursday, just a few hours after the outlawed IRA bombed a shopping mall in north London. Eleven people were injured.

The IRA has recognized the potential of the big-bomb tactic, and has tried to repeat it. Police seized a massive bomb, reported to contain more than one ton of explosives, in London on Nov. 14. A day later, they defused a van full of explosives outside the Canada Tower at Canary Wharf, the tallest building in the city.

Some who support the IRA's campaign of unifying Ireland by force believe economic disruption is the key.

''History teaches us that the British government can be highly motivated when it comes to matters of economic self-interest,'' said one strategist in the republican campaign in Belfast. He spoke on condition of anonymity.

Private homes can still be insured against terrorist attacks, although they are not typical targets, and vehicles can be covered. Some insurers will also provide up to $775,000 of coverage to small businesses, such as pubs, that have been IRA targets.

But insurers - who lay odds on damage from everything from burglaries to tornadoes - say terrorist attacks on big buildings pose too great a risk.

''In theory, there's nothing to stop a terrorist organization from saying, 'We're going to put bombs outside buildings every day this week,''' said John Wooden, spokesman for the Association of British Insurers. ''It's something that private enterprise cannot afford to take on.''