Karl Rove, President Bush"s top political adviser, is shown in this April 9, 2005. Ethics briefings were scheduled for staffers according to the first letter of their last name. If that practice is followed, Rove would be expected at a session at 4 p.m. on Wednesday. (AP Photo/Andy Manis)

Karl Rove, still under investigation for his alleged role in leaking the identity of an undercover CIA agent, faced possible implication in further scandal yesterday after the resignation of an ally accused of misusing public broadcasting funds for partisan political purposes.

Kenneth Tomlinson, a friend of the powerful presidential adviser for a decade, was forced to resign on Thursday as chairman of the Corporation for Public Broadcasting (CPB), where he set out to correct what he saw as liberal media bias. An internal report found he had overreached in those ambitions.

Yesterday it emerged that Mr Tomlinson is also under investigation by the State Department for possible abuses of power in a second job, as head of the federal agency overseeing government broadcasts to foreign countries. The New York Times reported he was suspected of diverting federal funds to further his partisan agenda at the CPB. The investigation is also looking at allegations that he put unqualified cronies and ghost employees on the federal payroll.

There was no suggestion that Mr Rove was implicated, but the State Department was reported to be looking at emails between the two men. President Bush remains under pressure to fire Mr Rove, his closest and most trusted adviser, because of his role in discussing the identity of the CIA agent Valerie Plame with reporters in the immediate aftermath of the 2003 invasion of Iraq.

Mr Rove has so far escaped indictment over the affair, but the special prosecutor has not ruled it out. The only resignation so far has come from Lewis "Scooter" Libby, chief of staff to Vice-President Dick Cheney, who pleaded not guilty last week to five counts of lying to investigators and obstructing justice.

The Plame scandal goes to the heart of the Bush administration"s rationale for war in Iraq because the leaking of her name was part of an apparent effort to discredit her husband, Joe Wilson, a former US ambassador who had publicly contradicted administration claims that Iraq was pursuing a nuclear weapons programme. Mr Wilson told The Independent on Sunday last week the blowing of his wife"s cover had been "an abuse of the public trust". The possibility of Vice- President Cheney testifying in the trial of one of his key staffers was "unseemly at least".