Wen Ho Lee has spent nine months in solitary confinement

But a judge in Albuquerque, New Mexico, told the court that the hearing would be delayed until Wednesday.

"I must regretfully say we cannot proceed with the hearing this afternoon," US District Court Judge John Parker told a court full of family and friends, who had come to see 60-year old Dr Lee released after nine months in solitary confinement.

Dr Lee's daughter, Alberta, left the packed courtroom in tears.

Charges

He was accused of transferring secret material to unsecured computer tapes - some of which have disappeared.

The welcome parties will have to wait for at least two more days

He was originally charged on 59 counts, and could have faced a life sentence.

Judge Parker twice delayed Monday's hearing to allow lawyers more time to work on the deal intended to lead to Dr Lee's release.

Dr Lee also promised to help the FBI verify his claims that he destroyed seven missing seven computer tapes of weapons data.

"The issue here is ... we find out what happened to those tapes. I think that is the key," US Energy Secretary Bill Richardson said, before the postponement was announced.

"The plea bargain enables us to get that information."

Sensitive

The three-year investigation has been marked by claims that the scientist - who was born in Taiwan - was unfairly singled out for investigation because of his race.

Wen Ho Lee's daughter keeps up the fight

Federal officials had suggested he had helped China to acquire American nuclear weapons technology developed at the top-secret Los Alamos research centre.

Mr Lee was originally denied bail on the grounds that he could pose a risk to US national security.

BBC world affairs analyst Nick Childs says the case of Dr Lee has been one of the most controversial and sensitive of its type in recent US history.

He lost his job against a background of widespread allegations that he had compromised what were described as "the crown jewels" of US nuclear weapons technology.

There were suggestions he had passed data on advanced US nuclear warhead designs to China, charges which helped sour what were already delicate relations between Washington and Beijing.

Since then, however, it has emerged the data involved was not nearly as sensitive as originally thought.