US media reports have said it appeared Harman agreed to intervene in the case in return for help in getting Democrats to appoint her to lead the House of Representatives Intelligence Committee, which she sat on.

Harman did not get the post after Democrats won control of congress in 2006 and left the committee shortly afterwards.

The reports said Harman was not the target of the wiretap.

Alberto Gonzales, the attorney-general under George Bush, the former US president, intervened to stop the investigation involving Harman in order to gain her support for the administration's policy of wiretapping without warrants, the Associated Press reported.

Lobby power

Hillary Mann-Leverett, a former US National Security Council official, told Al Jazeera the case "showed the power and influence of the pro-Israel lobby so much so that the pro-Israel lobby thought it owned the chairmanship of the committee on intelligence in the US congress and could sell it to Representative Harman".

Critics have said pro-Israel lobbyists have too
much influence on US politics [AFP]
Rosen and Weissman were charged in 2005 with conspiring to pass on US defence information to unauthorised personnel.

The material included information about al-Qaeda, the 1996 bombing of the Khobar Towers dormitory in Saudi Arabia that killed 19 US military personnel, and US policy towards Iran.

The two had worked until 2005 for the American-Israeli Public Affairs Committee, the leading pro-Israel lobby group in the US.

Their trial is scheduled to take place in early June at a Virginia federal court but is likely to be delayed further because the judge has a scheduling conflict.

'Abuse of power'

On Tuesday, Harman released copies of a letter she had written to Eric Holder, the current US attorney-general, repeating her denial of the claims and asking for the release of any tapes.

"I never contacted the department of justice, the White House or anyone else to seek favourable treatment regarding the national security cases on which I was briefed, or any other cases," Harman wrote.

A justice department spokesperson said the letter was being reviewed and had no immediate comment.

Harman called the official eavesdropping an "abuse of power" and told MSNBC any politician could be at risk.

"This isn't about me. This is about any member of congress," she said.

"Members of congress have been calling my office this morning asking whether perhaps in their own conversations with advocacy groups ... maybe they were inadvertently picked up on some kind of an eavesdrop with or without a warrant."