URANIUM mining is becoming the defining issue of the West Australian election as the major parties lock step on most other policies, leaving voters struggling to see the difference.

Premier Alan Carpenter yesterday stepped up his attack on the Liberal Party for its pro-uranium mining stance, claiming it was inevitable the state would become a nuclear dumping site if the Liberals were elected to power on Saturday.

But the Liberals hit back, with Opposition Leader Colin Barnett ridiculing Labor for apparently thinking nuclear waste came from mining.

"You do not get nuclear waste from uranium mining," he said.

"You get nuclear waste from nuclear power stations, and there is no prospect of a nuclear power station.

"At the time of the last Liberal government in 1999, a piece of legislation was passed through parliament which actually banned nuclear waste being dumped in Western Australia."

Mr Barnett pledged that a Liberal government would not allow nuclear waste to be dumped in Western Australia, and would not allow uranium to be transported through residential areas.

The issue turned ugly after Labor launched a stinging television advertisement at the weekend claiming Mr Barnett would allow uranium to be trucked past people's homes.

"Which schools and suburbs would the trucks be passing through? And where in WA are you going to bury the radioactive waste?" the advertisement asked.

"WA doesn't need uranium mining, and it doesn't need nuclear waste."

It then shows Mr Barnett saying: "Yes they do, they do."

The state electoral commission yesterday launched an investigation after the Liberals complained the ad was false and misleading and the quote from Mr Barnett was from unrelated footage.

Liberal Party state director BenMorton said it was a deliberate attempt by Labor to mislead the voters.

Electoral Commissioner Warwick Gately said he would examine the ad today.

But Mr Carpenter was unfazed.

"Anybody who thinks the international nuclear industry is not licking its lips at the prospect of Colin Barnett allowing mining of uranium, because they'll be able to get the waste taken back into Western Australia, anybody who doesn't believe that (is wrong)," he said.

Mr Carpenter seized on uranium as a potential winner last week when he abandoned his long-held refusal to enshrine the state's uranium mining ban in legislation, saying he now believed it was essential.

At Labor's campaign launch on Sunday, he followed up by saying a vote for the Liberals was a vote for uranium, while a vote for Labor meant clean, green renewable energy.

But Mr Barnett said Labor's green claims were rubbish and he was the greener of the two.

"During my time as an energy minister the use of natural gas for power generation in Western Australia went from 35 per cent to 60 per cent. We were by far the cleanest electricity producer of any Australian state," he said.

The Albany wind farm was built on his watch, he said, and he presided over the construction of the state's gas power stations and gas pipelines.