The survey, conducted by The New York Times and CBS News, found that the outcome of Tuesday's congressional elections could shift significantly, depending on which party's supporters go to the polls.

If turnout is average for a mid-term election neither side has a particular edge in the popular vote. But the poll showed that Republicans' prospects would surge if, as some analysts predict, turnout is unusually low.

"Usual" turnout is considered to be similar to the 1994 mid-term election when 37% to 39% of people voted.

The poll was based on telephone interviews with 942 registered voters from Monday to Wednesday. It has a margin of sampling error of three points in either direction.

The survey also showed that Americans view Republicans as more ethical but believe that Democrats are stronger on pivotal issues of education, health care and the future of Medicare and Social Security.

Ad campaign

That could explain why House Republicans unexpectedly launched a multi-million dollar advertising campaign that attacks Mr Clinton for his behaviour with Monica Lewinsky.

Democrats have fired back with a commercial of their own that emphasises issues -- and the need to move beyond the scandal.

The poll also counters claims that the White House sex scandal, which has hijacked the domestic political agenda since January, would not affect how the public voted.

Seven out of 10 polled denied that the scandal would have any effect on their vote.

In fact, President Clinton's appearances on the campaign trail appear to be helping mobilise voters.

At a gala dinner in New York for Senate candidate Charles Schumer the president got a standing ovation.

One attendant told BBC News: "I think everyone here felt the power of Clinton and how much he cares about America."

Another woman added: "He comes and he pulls the crowd. Did you hear a pin drop? Not a pin. He had them in his hands."