Mr Giuliani - who is almost certain to be running against Mrs Clinton for the Senate - was invited by Arkansas Governor Michael Huckabee.

Rudy Giuliani: "Proven Leadership for the Future"

According to the Republican Mayor's campaign website, Mr Giuliani will "attend a luncheon fund-raiser hosted by the Governor" as well as "taking in some of the famous sites in Arkansas and getting to know some of the people who live and work in the state".

Democrat activists in New York are not pleased.

"It's a cheap prank, unworthy of the mayor of the city of New York and a man who would be a U.S. senator," said Judith Hope, chairwoman of the New York State Democratic Committee.

"But it is typical of Rudy Giuliani."

Mr Giuliani's visit in seen by analysts as a way of satirising Mrs Clinton's anticipated bid for the Senate in a state where she has never lived and - until recently - spent little time.

But Mrs Clinton has been to New York dozens of times already this year, in the opening stages of a hotly-contested race - the first involving the wife of a president.

The First Lady was gently mocked on the front cover of New Yorker magazine, which depicted her walking innocently through Central Park with a tourist guide - while Mr Giuliani waits behind a tree, poised to mug her.

Campaigns pick up speed

Mr Giuliani - running under the slogan "Proven Leadership for the Future" - has made vigorous anti-crime measures a central part of his campaign.

But is she just a wide-eyed innocent ?

"Just a few years ago, the nay-sayers and pundits had written New York City's obituary," he says in a campaign newsletter; "together we've proved them wrong and today New York is a model city."

Mrs Clinton - campaign slogan "For All New York" - declares herself "a champion of children and families".