Nationals leader Brendon Grylls has offered preference swaps in exchange for $700 million a year for infrastructure projects.

The WA Nationals, who hold five of the 57 lower house seats, want 25pc of the royalties earmarked for infrastructure in resource-rich areas of the State.

Mr Grylls said his party wanted mining and petroleum royalties quarantined for regional electorates.

He said the royalties policy had been a Nationals platform for two years and would be a non-negotiable condition of any agreement to swap preferences with the Liberals.

He has threatened to take the offer to the Labor Party if the Liberals refuse it.

But Mr Barnett said he didn't do deals.

"I don't deal with preferences, that's a matter between the parties themselves so the Liberal Party organisation will no doubt discuss that with the National Party," Mr Barnett said.

"I'm not doing deals in the rush of an election campaign."

Mr Barnett said he wanted country people to vote Liberal first and he would not be part of a National Party stunt.