Defence secretary Nick Warner's hunt for the officials who reportedly conducted a covert investigation into Defence Minister Joel Fitzgibbon has been slammed by the Community and Public Sector Union and the Federal Opposition.

Mr Warner disclosed details yesterday of the massive investigation that since March 26 has involved more than 200 Defence staff being interviewed and more than 850 signing statutory declarations saying they had no knowledge of the unauthorised probe into Mr Fitzgibbon's relationship with wealthy businesswoman Helen Liu.

The union's deputy secretary, Michael Tull, said yesterday that Defence civilian personnel were ''deeply concerned'' about the conduct of the investigation.

''Defence civilian staff are heartily sick of being used as a football in someone else's political game,'' Mr Tull said.

''The CPSU is seeking an urgent meeting with Defence Department management to express these concerns.

''In particular, many people find the department's use of statutory declarations heavy-handed and vaguely insulting. Public servants take great pride in their trustworthiness and resent the implication that a statutory declaration is the only way to force them to tell the truth.''

Opposition defence spokesman Senator David Johnston dismissed the inquiry as ''meaningless'' and said Mr Warner's statements underlined ''the futility of the department investigating itself''.

Mr Warner defended the investigation headed by Defence chief security officer Frank Roberts, saying it was being conducted with ''total professionalism''.

''Technic al oversight is being provided by the Australian Security Intelligence Organisation. External security intelligence and law enforcement agencies have been consulted, and the Commonwealth Ombudsman has been briefed,'' he said.

Privately, Defence officials expressed resentment at the conduct of the inquiry, describing it as ''a waste of time'', ''a scatter-gun exercise'' and ''plagued with conflicts of interest''.