A US atheist's request to say "IM GOD" on his number plate has been denied by the state of Kentucky, which said it might distract other drivers, could spark confrontations and would be in bad taste.

Bennie L Hart says that by driving around with the "I'm God" message, he simply wants to spread his views about religion — that it's impossible to disprove anyone's claim to being God.

Mr Hart says he had the same plate for a dozen years when he lived in Ohio, without causing any problems.

Mr Hart has sued Kentucky's transportation secretary, Greg Thomas, on free speech grounds, asking a federal judge in Frankfort to strike down some Kentucky laws and rules for personalised plates.

"Under the First Amendment, government officials do not have the authority to censor messages simply because they dislike them," said William Sharp, legal director for the American Civil Liberties Union of Kentucky, which helped file the lawsuit.

"And in this instance, personalised licence plates are a form of individual speech equally deserving of First Amendment protection."

State Transportation Cabinet spokesman Ryan Watts said the agency did not comment on pending litigation.

Mr Hart, who moved to Kenton County in northern Kentucky in February, intends to reapply for the "IM GOD" plate, his suit said.

When Mr Hart was first turned down in March for the plate, an administrative branch manager for Kentucky's Division of Motor Vehicle Licensing cited state law and regulations forbidding vulgar or obscene personalised plates, the suit says.

That characterisation is "demeaning" to Mr Hart and his views and amounts to censorship, the suit says.

"I simply want the same opportunity to select a personal message for my licence plate, just as any other driver," Mr Hart said in an statement released by the ACLU.

"There is nothing 'obscene or vulgar' about my view that religious beliefs are subject to individual interpretation."

In April, Mr Hart said state officials gave other reasons for their denial: that it was not in good taste, might distract other drivers and potentially spark confrontations.

According to the lawsuit, state officials indicated their denial was backed by a US Supreme Court ruling that upheld Texas' refusal to issue a number plate bearing the Confederate battle flag.

The court said in the 5-4 ruling that Texas could limit the content of number plates because they were state property and not the equivalent of bumper stickers.

AP