Anti-terrorist police who arrested eight Libyans in a series of dawn raids in Manchester, England, yesterday, believe they may have thwarted the next wave of suicide bomb attacks on British and American forces in Iraq.

The suspects, picked up at the end of a year-long investigation centered on Manchester, are being held on suspicion of either encouraging Al Qaeda or helping to fund some of its atrocities.

But intelligence sources say that some of them may have been planning to fly out to Iraq as suicide bombers.

Some are regarded as so dangerous that police and Home Office officials are seeking their immediate deportation. In the meantime they are being held at police stations across greater Manchester.

The men were arrested during coordinated raids on 19 addresses in five force areas. Twelve of the addresses are in Manchester, three in Birmingham, and one each in Bolton, Liverpool, Middlesbrough, and London. Two of the men have previously been named as having terrorist links on a U.N. Web site.

One of these, Tahir Nasuf, 44, works for the Sanabel Relief Agency, which raises money for Muslims in poor parts of the world. The charity has an office in Levenshulme, Manchester.

The American Treasury department has claimed that Sanabel is a front for the Libyan Islamic Fighting Group, which in turn is said to have links with Al Qaeda.

In February the U.N. froze the assets of both Mr. Nasuf and the Sanabel agency. He has always maintained his and the agency’s innocence.

Yesterday police were standing guard outside the pebble-dashed, end-of-terrace house in Fallowfield that Mr. Nasuf shares with his wife and four children. His black Ford Mondeo had been removed from the street outside at dawn.

The wave of arrests, which began at 3 a.m., involved 500 police officers. They were coordinated by the anti-terrorist unit of Greater Manchester Police and supported by MI5 and immigration officials.

Anti-terrorist officers said they had succeeded in arresting all the suspects they had targeted. Two were held under the Terrorism Act 2000, the others on suspicion of being in breach of immigration laws.

Two other men arrested in an early phase of the operation were later released.

Forensic officers are expected to take a number of days to search the raided properties. They have already taken away a number of computers and storage disks for examination.

Intelligence sources confirmed that, as expected, they found no evidence of such noxious substances as ricin poison.

The chief constable of Greater Manchester Police, Mike Todd, emphasized that the allegations against the men still being held, concern terrorist activity outside Britain. “I want to reassure people that we are not talking about a direct threat to the U.K. We are talking about the facilitation of terrorism overseas. That could include funding and the provision of support and encouragement to terrorists.”

Intelligence sources suggested last night that some of those under arrest may have helped to recruit and train terrorists. They regarded the operation as a “pro-active strike” against people suspected of encouraging terrorism.

Anti-terrorist officers said that the timing of the arrests had been agreed before John Reid took over as Home Secretary.

Some of the intelligence is believed to have surfaced last June when police raided the Manchester home of a suicide bomber who had blown himself up in an attack four months earlier.

The man, a 41-year-old French national of north African origin, was the first person to travel from Britain to attack coalition troops in Iraq. He had spoken to friends at a mosque in the city of his desire to fight jihad, or holy war, in the Middle East.

In this case, intelligence was supplied by the Iraqi security services. The bomber was unknown to MI5 but fits the profile of the “jihadists” who went to fight for the greater Muslim cause in Bosnia, Chechnya, and/or Afghanistan.

Security sources suspect there is a European network that supplies fighters and suicide bombers to Iraq, though just a “trickle” set out from Britain.

During this morning’s raid a helicopter was seen hovering above Mr. Nasuf’s house shortly after three police vans pulled up outside.

Neighbors of a man arrested elsewhere in Manchester said he was often seen carrying computers into his home. Police also raided the offices of the Sanabel Relief Agency in Sparkbrook, Birmingham.