With time ticking down before the second presidential trial in US history and the first in 130 years, conservative Republicans were fighting a tentative proposal for a witnessless four-day proceeding.

What happens after Thursday -- when Chief Justice William Rehnquist swears in the body's 55 Republicans and 45 Democrats as jurors -- is still anyone's guess.

But the tentative plan would feature opening arguments ending with a `test vote' on whether Clinton's alleged offences in the Monica Lewinsky flap -- perjury and obstruction of justice -- warrant his removal from office.

If that ballot fails to win support from a two-thirds majority -- the number of votes needed to oust Clinton -- then lawmakers could adjourn the trial and consider formally rebuking him.

And with Republicans unable to oustClinton by a mere party-line vote, most Senators have said Clinton's removal is an extremely unlikely scenario.

Bipartisan support -- including key backing from Republican Senate majority leader Trent Lott -- has built for the plan, largely because the votes needed to oust Clinton are unlikely to materialise.

And Clinton's soaring popularity ratings -- respondents to a recent poll declared him the most admired man in America, ahead of Pope John Paul II -- have also given senators pause.

But the proposal plays poorly among conservatives who want more consideration of the charges against Clinton that the House approved just over two weeks ago.

``I would be very sceptical of bypassing what I think is our constitutional responsibility to have a full airing of the evidence,'' Republican Senator Kay Bailey Hutchison of Texas told CBS television on Sunday.

Senators could be trampling on the US Constitution if they voted to end the proceeding without undertaking a genuine trial, warned Republican SenatorPhil Gramm, also of Texas.

``Seems to me, we're too preoccupied with what is good politics for senators, and not enough preoccupied with what we should do to fulfill the constitutional process,'' he said on NBC television on Sunday.

But those comments came as a large number of Democrats and an as-yet unknown number of Republicans back the option calling for opening the trial and swiftly concluding it.

Under a proposal from Democratic Senator Joseph Lieberman and his Republican colleague Slade Gorton, Senators would be sworn in this week.

The 13 House-appointed `managers' who will act as prosecutors in the trial would then have Monday, January 11, to make their case, with the White House making its day-long defence on Tuesday.

Senators would then have one day, Wednesday, to ask questions of both sides. No witnesses would be called, and on Thursday the Senate would vote on whether the charges -- even if proven -- rise to a level warranting Clinton's ouster.

The Senate would adjourn the trial andbegin considering censure -- a formal rebuke of Clinton -- if the 67 votes needed to oust the President aren't there.

Meanwhile, a handful of Democrats oppose even opening a trial on the grounds that, even if true, the allegations against Clinton do not meet the criteria for ousting the President.