The cryptic letter and CIA statement came on the eve of a House debate on an intelligence bill. The debate is expected to revive a partisan argument that has raged on and off for months about whether House Speaker Nancy Pelosi knew in the fall of 2002 about the CIA's use of waterboarding weeks earlier.

Waterboarding is an interrogation technique the CIA used on three prisoners in 2002 and 2003. It is a form of simulated drowning that President Barack Obama has called torture.

Congressional aides expect much of the debate on the House intelligence bill to be diverted into a discussion of what Mrs Pelosi knew about the CIA's harsh interrogation program and why, if she was briefed on it, she didn't formally object to it.

Republicans on the Intelligence Committee say the letters and Mr Obama's threat to veto the legislation are cover-up attempts on behalf of Mrs Pelosi and what she knew and didn't do about 'enhanced interrogation.' 'The blatantly political nature of the Democrats' letters is revealed by their handling,' said Jamal Ware, spokesman for Republicans on the committee, in a statement late Wednesday.

'One was slipped under a staffer's office door late at night, the other was deliberately hidden from Republican members for two weeks and had to be obtained from the press. It is unfortunate that the president's veto threat and the continued attacks by partisans against the CIA are a direct result of congressional Democrats' continued heavy-handed attempts to cover up for Speaker Pelosi.'

Mrs Pelosi told reporters in May she had not been informed that waterboarding had been used against terrorism suspects, even though it had been. When asked whether she was accusing the CIA of lying to her, she said, 'Yes.'

The CIA sent lawmakers a chart in May describing the 40 congressional briefings it gave on the interrogation techniques. But that document was found to include several errors, leaving in question exactly what Mrs Pelosi was told.

The Republicans seized on her accusation that the CIA misled Congress, contending that the California Democrat's remarks have demoralized the intelligence community. House Republicans have repeatedly demanded that a bipartisan panel investigate her allegations.

Rep Rush Holt, one of the Democratic authors of the June 26 letter to Mr Panetta, said the June revelation to the committee bolsters Mrs Pelosi's case.

'If people are saying, 'Heaven forbid the speaker said the CIA deceived Congress'- anyone who has served any time on these committees and is straightforward will say, 'Yes, of course,'' Mr Holt told the AP.

House Republicans oppose at least one provision in the intelligence authorisation bill, and they have an unusual ally: the White House.

Mr Obama's aides have said they will recommend he veto the bill if it includes a Democratic-written provision requiring the president to notify the intelligence committees in their entirety about covert CIA activities.

Under current law, the president is only obligated to notify the top Democratic and Republican leaders of the House and Senate and the senior Democratic and Republican members on each chamber's intelligence committee.

Democrats want to open the briefings to all members of the House and Senate intelligence committees unless committee leaders agreed otherwise. That would be about 40 lawmakers, depending on shifting membership rosters, instead of the eight required by law.

They claim the Bush administration sought to undermine congressional oversight. However, the White House is concerned that briefing more lawmakers might compromise the most sensitive US intelligence operations. -- AP