SYDNEY, Oct 7 (AFP) - Security surrounding Australia's general elections will be the tightest in history amid fears Al-Qaeda linked terrorists will try to disrupt the polls in hopes of ousting the US-allied government of Prime Minister John Howard.

After the 2002 Bali bombings and last month's Jakarta embassy blast, police say that this Saturday's vote will be marked by intense security preparations, although much of it will be carried out virtually unseen.

Parallels have been drawn between the Jakarta attack and the Madrid train bombings of last March which occurred on the eve of an election and helped hand victory to the Socialists, who withdrew Spanish forces from Iraq.

Australia's opposition Labor Party has made a similar election pledge, while Howard's pro-war government has vowed to keep troops in Iraq "until the job is done".

Calls from Al-Qaeda and sympathetic Islamic militants to target the United States' allies in the war in Iraq have prompted concerns of another attack aimed at swinging the vote.

"I think we are probably going to be finding it one of the toughest security regimes that have been mobilised," said John Bruni, a terrorism expert at the University of Adelaide. "There is certainly a sense of heightened security."

Although no terrorist attack has been carried out on Australian soil, the Jakarta embassy attack and the Bali bombings, which killed 88 Australians, have made security agencies wary. Would-be terrorist cells have been uncovered within Australia.

In May, Australian national Jack Roche, a convert to Islam, was jailed for nine years in Perth under new anti-terror laws over a plot to bomb the Israeli embassy in Canberra. During the trial it was revealed that British-born Roche underwent explosives training with Al-Qaeda in Afghanistan, and had met Osama bin Laden and as well as senior operatives of the Southeast Asian terror network Jemaah Islamiyah, the group blamed for the Bali and Jakarta embassy attacks.

Roche was told by Al-Qaeda's hierarchy to form a Caucasian terrorist cell in Australia.

Last year Frenchman Willie Brigitte was deported, and has been linked to international Islamic extremists. Brigitte, who married a former Australian soldier while in Australia, has been held under France's anti-terror laws since.

To forestall potential attacks, police and other security agencies have reactivated a Police Operations Centre created for the 2000 Sydney Olympics. Specialist tactical operations units, increased patrols of transport routes and polling booths are some of the measures, although few details have been divulged publicly.

Airports, transport networks and areas where large crowds might gather will be a prime focus on Saturday, while trucks will be on standby to help ambulances in the event of disaster. New South Wales state police commissioner Ken Moroney said increased visibility of police on the street was a key focus.

Howard has been keen to promote security awareness for electoral reasons as well. The prime minister has consistently sought to portray Labor opposition leader Mark Latham as weak on security, an area where polls show the conservative government has a firm advantage in the public mind.

The government has carpet-bombed the electorate with a second round of anti-terrorism advertising that urges people to "Be Alert, Not Alarmed."

Howard has been selling the anti-terrorism message hard in the final days of campaigning, warning Australians not to become complacent and claiming another attack in South-East Asia was "a near inevitability".

Terrorism expert Bruni, however, said that many of the most important security measures for the voting would be carried out behind the scenes.