LONDON (AP) _ Customs officials said they foiled an attempt on Wednesday to supply Iraq with 40 U.S.-made devices for triggering nuclear explosions, and that three people were charged.

U.S. and British investigators worked on the case for 18 months.

The Customs and Excise Department in a statement named the three as Lebanese engineer Toufic Fouad Amyuni, 37; Ali Ashour Daghir, 49, a company director with dual Iraqi and British nationality; and export executive Jeanine Celestine Speckman, 41, a Frenchwoman married to a Briton.

The statement said they were charged under the Export of Prohibited Goods Control Act and will appear before Uxbridge Magistrates Court in west London at 10 a.m. Thursday. All three gave addresses in or near London, it added.

Iraqi diplomats in London refused to comment on the case.

An investigation initiated by U.S. customs climaxed in a freight shed at London's Heathrow Airport as an attempt was made Wednesday morning to put the devices - which may have been dummies - aboard an Iraqi Airways flight to Baghdad, British customs officials said.

Authorities said five people were arrested in and around London, including Iraqi national Omar Latif, who was immediately served with a deportation order, and a Cypriot with a British passport who was released after questioning.

In Washington, the U.S. Customs Service said sealed indictments had already been returned at a San Diego District Court.

After the arrests, President Bush expressed concern over the spread of nuclear weapons in the Middle East and said in a written statement: ''We again call upon nuclear suppliers to exercise special restraint in providing materials related to the development of nuclear, chemical and biological weapons and intermediate-range missiles in this volatile area.''

While avoiding direct criticism of Iraq, Bush noted it was among the nations that signed the nuclear non-proliferation treaty.

Customs officials in London, speaking on condition of anonymity, said the devices were capacitors, electrical components of the detonation chain of a nuclear bomb.

Defense experts said it demonstrated Iraq's determination to become a nuclear power, even at the risk of being caught violating Western bans on the export of strategic high technology.

Indications emerged, however, that the devices deposited at Heathrow were dummies, substituted for the real hardware as part of the U.S. customs operation.

British Broadcasting Corp. TV said customs officers made the switch after the packages arrived from the United States at the beginning of the week. Channel 4 TV News carried an interview with the manufacturer of the so-called krytrons, who said his company turned over dummies to U.S. customs late last year.

''We provided about 40 devices ... to the Customs Service and they were deliberately made to be inoperative,'' said Don Kerr, president of EG & G in Wellesley, Mass.

He indicated he did not know whether these were the devices that reached London, saying: ''Basically we supplied these devices to the Customs Service in the United States and the subsequent movement of them is unknown to us.''

The Home Office said Latif was to be deported because of ''attempted breaches of legislation governing the export of strategic goods from the United Kingdom.''

BBC-TV showed footage of the operation that it said was shot by an NBC crew that was in on the investigation.

NBC reported Scotland Yard detectives raided the headquarters ''of what is being described as a secret Iraqi nuclear procurement network,'' and removed documents and other evidence.

It quoted authorities as saying ''the man at the top of the Iraqi operations is Ali Daghir, who was sent to London from Baghdad almost two years ago.''

NBC said Daghir was arrested at his office shortly after the Iraqi flight took off.

British officials made few formal statements about the incident.

U.S. customs spokesman Ed Kittredge commented, ''They're sensitive about Iraq and the number of British citizens there.''

Kittredge mentioned Iraq's execution March 15 of Farzad Bazoft, an Iranian reporter who was working for a British newspaper.

Iraq accused Bazoft of spying. Britain reacted by withdrawing its ambassador from Iraq and expelling some Iraqis, but it has been reluctant to let relations with Baghdad worsen further. More than 10,000 Britons work in Iraq.

The Foreign Office summoned the Iraqi ambassador to inform him of the expulsion but refused to link the action to the alleged smuggling operation.

Military experts said the devices are available only to a handful of major powers, and their export is strictly controlled. They recalled two previous smuggling attempts, one involving Israel and the other Pakistan, both of which have nuclear weapons ambitions.

Iraqi President Saddam Hussein is known to harbor ambitions of eclipsing Egypt and Syria as the premier military power of the Arab world. In 1981, Israeli warplanes bombed an Iraqi nuclear reactor, claiming it was designed to make bombs. Lately, Iraq has developed long-range missiles thought to be capable of delivering a nuclear warhead.

Professor Paul Wilkinson, a Bradford University terrorism expert, said: ''If they're trying to smuggle in these highly sophisticated trigger devices, that means they're very serious about making nuclear weapons, and soon.''