And it now looks increasingly likely that Mr Clinton may escape a formal censure motion as well as removal from office.

A ballot, expected on Thursday or Friday, will almost certainly fail to reach the two-thirds majority needed to remove him - as Republican prosecutors appear to have failed to convince Democrat senators to vote with them.

At least 12 Democrats must join the 55 Republican senators to achieve the 67 vote threshold.

The focus of deliberations is now likely to move to possible censure motions, although once again there are doubts as to whether any such motion would gain sufficient support.

Correspondents say it leaves the prospect of President Clinton walking away from his impeachment ordeal with an acquittal and no official rebuke from the Senate.

No cameras

Earlier on Tuesday, senators decided to switch off the cameras and clear the public gallery to hold their final debate on the fate of President Clinton behind closed doors.

The BBC's Catherine Martson reports: Vote could take place as early as Thursday

A motion to open deliberations to the public received 59 votes in favour with 41 against, falling short of the 67 votes required under rules drafted during the only other impeachment trial against President Johnson 131 years ago.

Democrats had given their overwhelming support to the motion, and were backed by a number of Republicans senators.

But the Republican leadership came out against the idea, believing privacy would encourage brevity and bring the proceedings to a speedier conclusion.

The debate procedure - the next stage in the impeachment process - gives each one of the 100 senators the opportunity to talk for 15 minutes.

"I hope that we won't just have speeches, that in fact we will have deliberations," said Majority Leader Trent Lott who had opposed the motion to open the debate to the public.

Efficiency measure

Washington Correspondent Philippa Thomas: A lot of senators want to get back to business

Shortly afterwards the senate voted unanimously to allow senators to make public their speeches by placing them into the official trial record.

The BBC's Washington Correspondent, Phillippa Thomas, says there is a feeling among senators that continuing the debate in private would make their deliberations "more efficient and more measured".

Everybody wants to move on, our correspondent says, to focus on what the president refers to as "the nation's business", freeing up congress to concentrate on other matters.

Formal rebuke

Democrat senators have been pushing for an alternative punishment for the president in the form of a sternly-worded formal rebuke - or censure - of his behaviour, to be taken up by the Senate after the trial proper.

They have already drafted such a motion that they could support as an alternative to impeachment.

The Lewinsky tapes do not seem to have swayed Senators

The proposal states the president "gave false or misleading testimony and impeded discovery of evidence in judicial proceedings".

It would leave the president open to future criminal and civil actions.

Some commentators are suggesting that Independent Prosecutor Kenneth Starr, who wrote the exhaustive report into the president's alleged wrongdoings could continue to bring a case against Mr Clinton.

But Republican senators are showing reluctance to support such a motion in the event of President Clinton being acquitted of both impeachment charges.

They say Democrats only want a censure motion to persuade the electorate that they do not condone the president's behaviour.