As senators were given their chance to question prosecutors and defence, Senator Byrd of West Virginia said he would offer a motion on Monday to have the trial dismissed.

"I plan to make this motion not because I believe the president did no wrong, in fact I believe he has caused his friends, family and the nation great pain," he said.

Mr Byrd is known for his non-partisan commitment to the Constitution and procedure, and Republicans are known to have been looking to him for guidance on how to proceed with impeachment.

The BBC's Clive Myrie: "Most Republicans have reached the conclusion that a conviction is impossible"

The senator, who has been critical of President Clinton's conduct in the Lewinsky affair, said the 67 votes necessary for convicting the president were not there; continuing the trial would "only prolong and deepen the divisive, bitter and polarising effect that this sorry affair has visited upon our nation".

Questions and answers

After listening to defence and prosecution presentations for two weeks, senators had their first chance on Friday to become more actively involved.

The senators had 5 hours on Friday, with a further 11 on Saturday to put queries through the judge, before voting on Monday whether to dismiss the case or call for witnesses.

On Friday, Republicans used their questions to advance their arguments for calling witnesses, asking why the defence team has avoided certain compelling reasons why witnesses should be called.

Prosecutors described some of the president's testimony as evasive and misleading, and went into fine detail on discrepancies between the testimony of President Clinton's secretary Bettie Currie and Monica Lewinsky.

Prosecutor Asa Hutchinson answers a question disputing the quality of the Grand Jury testimony

White House counsel Charles Ruff said it was "wishful thinking" that testimony before the Senate would make any difference to the existing evidence.

Rep Ed Bryant of Tennessee, one of the prosecutors, seized the opportunity to answer the first question, which had asked if the president's lawyers had mischaracterised any issues in their presentation.

Stephen Sackup talks to BBC World

"There are a number of mischaracterisations and statements that we disagree with that the president's defence team made," Mr Bryant said.

He said the president's lawyers had left out important evidence that would have provided "ample corroboration," arguing that Monica Lewinsky's testimony was verified by White House records, phone logs and the testimony of her friends and Secret Service agents.

Answering the first Democrat question, White House Counsel Charles Ruff said Mr Clinton's defence team had laid out specific instances where they disagreed with the prosecutors' conclusions, but were not broadly condemning those conclusions.

All sides are now engaged in behind-the-scenes manoeuvres over Monday's vote, which could prolong the hearing for months or bring it to a swift conclusion.

However, BBC Washington Correspondent Paul Reynolds says that whatever happens, most people believe the president will not be convicted of the charges of obstruction of justice and perjury.

Democrats delighted

Democrats have been pleased by the strength of the president's defence, which closed on Thursday.

Even Republicans praised a highly emotional speech by Mr Clinton's long-time friend Dale Bumpers.

"You're here today because the president suffered a terrible moral lapse, a marital infidelity. Not a breach of the public trust, not a crime against society," he told the senators.

The BBC's Stephen Sackur: "Some believe the White House lawyers have done a very good job"

Speaking at the end of the defence presentation, he asked senators to give the public a break.

"The American people are now - and for some time have been - asking to be allowed a good night's sleep. They're asking for an end to this nightmare. It is a legitimate request," he said.