The military judge presiding the pre-trial hearing of the US soldier charged with leaking classified data to Wikileaks rejected Friday a defense request to hear from eight witnesses they claim are "essential" to the case.

Bradley Manning, 24, appeared in court for less than an hour Friday at this military base north-east of Washington on the second day of a preliminary hearing considering three defense motions seeking access to incriminating evidence.

Manning, who served as a low-ranking intelligence analyst in Iraq, has been charged with 22 counts in connection with turning over a massive cache of classified US documents to the secret-spilling website WikiLeaks between November 2009 and May 2010.

Manning's civilian lawyer, David Coombs, submitted the names of eight people, including two civilians, who were in charge of classifying the documents that Manning allegedly leaked.

Those people include Under Secretary of State Patrick Kennedy and Rear Admiral David Woods, the current head of the prison at the US naval base in Guantanamo Bay, Cuba.

Coombs, who claims their deposition is "essential and necessary" for Manning's defense, want the officials to describe the impact of the Manning's alleged leaks on US national security before the court martial begins.

The defense claims that Manning's alleged leaks did not have a significant national security impact. Coombs also wants to ask them about the way that documents are classified in the first place.

The prosecution claims the leaks aided a US enemy, specifically the Al-Qaeda terror network.

On Thursday the prosecution claimed that testimony from the officials is "not relevant," and that the officials in question are "not reasonably available" to testify.

Judge Denise Lind agreed with prosecution arguments that these depositions were required only for key witnesses which may be unavailable at the time of the trial.

But these officials could still testify at Manning's courts-martial. The government has asked that the trial begin on August 3, while the defense wants it to begin in June.

At a preliminary hearing in December Coombs submitted a list of people he wanted to hear from. The request was rejected, but on Thursday Coombs asked Judge Lind to reconsider.

The government had unilaterally decided that these "vital witnesses" could not attend the hearing even though they had not been asked, Coombs said.

"The government is fighting Coombs every inch of the way, and it feels like the judge really wants to rule against Manning," said Kevin Zeese with the Bradley Manning Support Networks at the Thursday hearing.

Manning has not yet entered a plea.

His next court appearance is on April 23.