The report, due for release on Tuesday (1430 GMT), is thought to have the potential to cause as much damage to the Clinton presidency as many fear has already been done to America's defence interests.

The BBC's Duncan Hewitt: The reaction in Beijing was swift and angry

Most of the report's findings have already been leaked, including the revelation that China is now thought to possess detailed information on every nuclear warhead in the US arsenal, including neutron bombs.

"Thefts almost certainly continue to the present," a copy of the report, leaked to the Associated Press (AP) news agency, is quoted as saying.

High-level knowledge

The three-year investigation, led by Republican Congressman Christopher Cox, concludes that despite high-level knowledge of the leaks, little was done to tighten control on sensitive information, and security still falls short of minimal standards.

The BBC's Duncan Hewitt in Beijing: "Tensions look set to grow"

As a result, the report says, Beijing's strategic nuclear capabilities were catapulted from 1950s-style technology, to being "on a par" with America's, in just a few years.

It adds that two land-based and one submarine-based weapon system have the capability to reach the US mainland, and China may be able to begin a device later this year.

The BBC's Tom Carver: "A damning indictment of America's ability to protect her own secrets"

Beijing has rejected the report as "groundless" and "highly exaggerated", even before its official publication. It accuses the US of faking information in order to damage China's credibility.

Serious breach

Many analysts say the case appears to be the most serious breach of nuclear security since the Soviet Union stole atom bomb secrets in the 1940s.

President Clinton says he was never told of the leaks

The depth of the scandal increased at the weekend when a senior government official, Notra Trulock, said he had informed the White House three years ago that he was convinced China had spied on American nuclear facilities.

Earlier this year, Mr Clinton said during his time in office no one had told him of suspected nuclear espionage.

BBC Washington Correspondent Tom Carver says the fact that this sort of espionage appears to have been going on for so long is a damning indictment of America's ability to protect its secrets.

Weapons laboratories

The report says there have been serious breaches at the Los Alamos weapons laboratory

The fallout from the report is almost certain to have an impact on the operation of America's weapons research laboratories, which at present are managed by the Department of Energy.

Energy Secretary Bill Richardson is expected to announce a series of disciplinary measures against staff within the next few days.

But there are growing calls for more senior heads to roll, including that of Attorney General Janet Reno.

She is under fire for refusing to authorise FBI requests for a communications tap on Taiwanese-born scientist Wen Ho Lee.

Sacked from his position at the Los Alamos weapons research laboratory, he is suspected of passing nuclear secrets to Beijing, although he has not been charged with any crime.

Senior Republicans have labelled Ms Reno's handling of the case as "indefensible". She says she is staying put.

Submarine technology

Submarine detection technology is also thought to be involved

China is also thought to have acquired details of electromagnetic devices, which could be used to disable satellites and missiles, and submarine-detection technology, potentially affecting the security of the UK's Trident fleet.

According to AP, the report also picks out two US companies - Loral and Hughes Aircraft - which went "outside the scope" of their export licences to provide China with information, helping to improve the reliability of nuclear missiles.

It says China may have set up around 3,000 "front companies" to act as conduits for technology used in the development of advanced weapons.