WASHINGTON - Republicans have been dealt a fresh blow by the publication of a new poll which suggests the Democrats are leading in 11 of 15 crucial races for the House of Representatives - the clearest indication yet that the party's stranglehold in Washington may be about to end.

Senior party members are concerned that fallout over the scandal involving a Republican Congressman sending sexual email messages to a teenage Capitol Hill intern and growing public concern about the war in Iraq could result in Democrats seizing the House - and also the Senate - in November's mid-term elections.

As the scandal over former Congressman Mark Foley's sending of the messages entered its sixth day, one Republican warned that there may even be further disclosures involving other politicians.

So far the scandal has resulted in the resignation of only Foley, who promptly placed himself in a clinic for alcoholics and drug addicts and claimed through his lawyer that as a boy he had been sexually assaulted by a priest.

Despite a number of calls for him to step down, the Speaker of the House, Dennis Hastert, has refused to stand aside and has received the public backing of President George W. Bush.

But the new poll, conducted for Reuters by Zogby International over a six day period, places Democrats ahead in 11 key congressional contests. Pollster John Zogby said: "This is a dismal showing for Republicans. Republicans ought to be very, very nervous."