NEW YORK – Rudy Giuliani never shrank from defending his image as mayor, but as a businessman he’s gone a step further – even trademarking his own name, the New York Daily News has learned.

The unusual step, revealed in a recent Giuliani company contract obtained by The News, states under the heading “Use of Mr. Giuliani’s Name” that the “trade names and trademarks “Rudolph Giuliani,’ or “Giuliani Partners LLC’ … shall not be used … without prior written consent.”

Doing anything that “tarnishes, degrades, disparages or reflects adversely on the Giuliani” name, it adds, will be grounds for terminating the contract.

As Giuliani now ponders a run for the White House, the document underscores what has become a central question of his candidacy – how will the former mayor’s roster of mostly private business clients play when viewed through the harsh prism of presidential campaign politics?

It is clearly something the mayor’s own people are worried about: In a list of potential “problems” written inside a Giuliani campaign dossier and obtained by The News recently from a source sympathetic to a rival campaign, the word “business” appears at the top of the list, above even his ex-wife, Donna Hanover.

Apparently, Giuliani’s own aides are already imagining the negative ads that could spring from his business dealings.

In the five years that Giuliani has worked in the private sector, his clients have run the gamut, from gambling interests like the National Thoroughbred Racing Association, which may further trouble Christian conservative voters, to large power-generators like the Atlanta-based Southern Co., which environmentalists regard as among the worst polluters in the nation.

He has lent his name to every corner of the energy industry – representing nuclear, oil and natural gas concerns – and worked with the pharmaceutical industry to keep cheap prescription drugs from flowing into the U.S. from Canada.

And that’s just what is publicly known.

Giuliani Partners and its subsidiaries are all privately held companies, and the former mayor has refused to release a full client list – making a clear analysis of his net worth impossible, and very likely raising disclosure questions, should he run for president.

“We are reviewing that right now,” Giuliani spokeswoman Sunny Mindel said when asked if the former mayor planned to release his client list. “But I would reiterate that voters are sophisticated enough to distinguish between public sector and private sector, and they know leadership when they see it.”

Forbes magazine estimates that the mayor’s companies have reaped “tens of millions of dollars” in contracts, to say nothing of the mayor’s estimated $8 million in annual speaking fees and his $3 million in book advances.

His empire includes the flagship Giuliani Partners LLC, a corporate consulting firm, and Giuliani Safety & Security, which has provided security advice to everyone from the Indian Point nuclear power plant in Westchester County to the government-backed Asian Games in Qatar, a Middle East emirate.

In 2005, Giuliani also became a named partner at Bracewell & Giuliani, a Texas-based law firm with a large legal and lobbying arm, much of which is aimed at protecting coal- and oil-burning electrical plants from further government regulation, experts say.

“There were a lot of eyebrows raised in Washington when Mr. Giuliani decided to become a named partner, because Bracewell really does represent some of the most notorious polluters in the U.S.,” said John Walke, clean air director for the Natural Resources Defense Council.

Bracewell officials declined to comment but have long argued that their clients are dedicated to providing clean, affordable power.

At the top of this corporate empire is Giuliani himself, whose image as “America’s Mayor” has proven as bankable financially as it is politically. “Business is excellent,” said Michael Hess, the senior managing director of Giuliani Partners and a former city corporation counsel under Giuliani. “Almost all of our engagements have worked out beautifully.”

Hess acknowledged that some of Giuliani’s portfolio could pose political challenges if he runs for president, but he argued that there is almost no major corporate interest today that does not attract its share of detractors.

“Someone could say, “Gee, we don’t like them,”‘ Hess told The News. “But if you take that to the logical extreme, you’d end up not doing business with anyone.”

As for the trademarking of Giuliani’s name, Hess said it was simply “a proper precaution” to prevent the unauthorized use of one of America’s most distinctive names.

“If you say “Rudy,’ everyone thinks of Rudy Giuliani,” said Hess. “If you say “John,”‘ added Hess with a sly nod to one of Giuliani’s likely Republican opponents, “you don’t necessarily think of John McCain.”