Washington - On the next-to-last weekend before historic US elections, Republicans were dialling voters to deliver hate messages that imply Democrat Barack Obama is a terrorist in a frantic effort to revive John McCain's stalled campaign.

Meanwhile, Obama, 47, held court before 100,000 at Missouri's Gateway Arch Saturday, revelling in the growing support in this one- time stronghold of centre-right Republicanism.

The contrasts underlined the advantage that two major polling groups gave Obama on Saturday: Rasmussen poll favoured Obama 50 per cent to 45 per cent, and Gallup, 50 per cent to 42 per cent.

Yet Obama, who hopes to become the country's first black president on November 4, had a message for "Democrats who are getting cocky."

"Democrats have a way of snatching defeat from the jaws of victory," he told the Missouri crowd. "You can't let up. You can't pay too much attention to the polls. We have to keep fighting for every vote."

Expectations built as former secretary of state Colin Powell, the Republican African-American general who served in the first Bush administration, indicated he will share his views on the election campaign on NBC's Meet the Press Sunday morning at 1300 GMT.

Powell, a reluctant supporter of Bush's war in Iraq, was once regarded as a potential Republican presidential contender.

The Republicans' anti-Obama phone campaign - dubbed "robo" calling for the automatic dialing it involves - was reminiscent of underhanded tactics used by President George W Bush in 2000 to defeat McCain for the Republican nomination by making innuendos about the parentage of the McCains' adopted Bangladeshi child.

This time around, the campaign of the 72-year-old Vietnam war hero is doing the smearing, telling voters in battleground states like Virginia, Ohio and Florida that Obama "has worked closely with domestic terrorist Bill Ayers, whose organization bombed the US Capitol, the Pentagon, a judge's home and killed Americans."

One upset recipient, a woman in Havertown, Pennsylvania, told the Philadelphia Inquirer daily that when one listened to it, "you get the impression that Obama himself is a terrorist."

The robocalls have brought condemnation from within McCain's own Republican ranks.

Maine Senator Susan Collins Saturday said the calls "don't serve John McCain well" and told a Maine political news website, politickerme.com, that "the people of Maine want to hear of John McCain's plans for the country, and not about Bill Ayers."

Obama was only 8 or 9 years old when Ayers, now a professor of education at the University of Chicago and an advocate for education reform, helped found the 1960s radical anti-Vietnam war group, the Weather Underground.

The group attacked federal buildings in Washington, but the attacks Ayers was involved with did not result in any deaths. Ayers escaped conviction.

Obama lives in the same Chicago neighbourhood as Ayers and served on two education reform projects with the one-time militant during the past 10 years.

Ayers also hosted a meet-the-candidate night for Obama when the Democratic nominee was running for the Illinois state legislature.

Obama has repeatedly disputed McCain's charges that Ayers is a campaign advisor, saying the Republican's focus on Ayers "says more about" McCain's campaign "than it says about me."

Obama campaign officials say the robocalls are a sign of desperation in the Republican's campaign.

Obama's running mate, Senator Joe Biden, said in Nevada Friday that the robocalls "don't' hurt Barack Obama ... but they hurt the American people because they attempt to distract you from the serious issues in our daily lives."