By Andrew Webster in Melbourne

If there are two things that can be said to mark an Australian summer, they are the beach and cricket.

South Africa's Makhaya Ntini has been abused in Australia

But this year, both Aussie iconic pastimes have been marred by a series of racist incidents that have shocked most people and threatened the future of international cricket tours down under.

By far the most serious was also the first. More than 30 people were hurt in early December's race-related riots and reprisal attacks in and around Cronulla beach in Sydney.

Politicians, including cricket-loving Prime Minister John Howard, were quick to reject accusations the riots showed racism is on the rise in Australia.

Instead, the unrest has essentially been blamed on simmering local tensions.

On one side were the largely white residents of the city's southern beachside suburbs.

On the other, were the Sydney-siders of Middle Eastern descent who visited the beaches at weekends.

The weak-minded minority might think again if they realised they faced bans or huge fines Cricket Australia's James Sutherland Read more

Less violent, but in some ways more disturbing, have been the growing number of racist taunts that have since sullied international cricket grounds throughout the summer.

Perhaps spurred on by the alarming images a week earlier in Cronulla, spectators at the first Test in Perth subjected some members of the South African cricketers to crude apartheid-era insults.

Fast bowler Makhaya Ntini and several other players were called "kaffirs" and "kaffir boetie" (brother of blacks) by people in the Waca crowd.

Although the remarks were widely condemned, there was a suspicion that the culprits may not have been Australian.

After all, Western Australia has a lot of white South African immigrants.

INCIDENTS AT GROUNDS IN 2005/06 11-14 Dec: South African players complain of racial abuse during first Test in Perth 2-6 Jan: Andre Nel complains of racial abuse while fielding in third Test in Sydney 10 Jan: South Africans again abused during warm-up for one-day game at the Gabba, Brisbane; one spectator ejected 20 Jan: Spectator at Melbourne's Telstra Dome ejected after reportedly punching an ICC official and accusing him of being South African 26 Jan: Sri Lankans abused at Adelaide Oval; five spectators ejected

But the theory that racism in cricket may be geographically isolated or simply un-Australian has since been shown to be false.

During the Test series with South Africa and the current one-day VB Series that also features Sri Lanka, every single one of Australia's major grounds has experienced similar racial abuse.

Sri Lanka did not formally complain at the Adelaide Oval when their players were abused, but five offenders were identified and swiftly ejected from the ground.

The South Africans have found the experience so painful that they have even spoken of ending their tour early and not coming back.

Recognising the seriousness of the situation, Cricket Australia chief executive James Sutherland has called for urgent action.

He wants the nation's legislators to pass measures allowing heavy fines and life bans to be levied on the "half-a dozen half-wits" he says are to blame.

And he points out that "nearly one million Australian spectators have offered a warm and enthusiastic welcome to South Africa's, West Indies' and Sri Lanka's cricketers this summer".

The Australia team has a reputation for playing hard and sledging their opponents to gain a psychological edge.

Aussie captain Ricky Ponting has hit out at troublesome fans

But they stop well short of racism and have made it clear that there is no place in the game for spectators who cross the line.

South Africa captain Graeme Smith wants cricket to take the racist issue as seriously as football's rule-makers.

That may yet happen. The International Cricket Council has announced it will investigate the allegations by sending India's solicitor general to Australia to compile a report.

Sutherland said he expects the fallout from the report to raise the question of possible sanctions against countries seen to have a problem with racism.

Possible action might include restrictions on those grounds with a poor record of crowd behaviour.

Whatever happens, with the one-day series yet to be concluded, it promises to be a nervous few weeks for Australian cricket.