WASHINGTON (Reuters) - Islamic extremist Osama bin Laden is bold, ruthless and should not be underestimated as the United States undertakes the fight against terrorism, former President Bill Clinton said on Tuesday.

Clinton, speaking publicly for the first time in detail about his own failed attempts to bring the Saudi-born dissident to justice, portrayed bin Laden as an evil but "worthy adversary."

"He's very scary. He's smart, he's rich, he's ruthless, he's bold ... with a very definite political agenda," Clinton said in a speech to Washington executives and opinion makers at the Kennedy Center.

Bin Laden is the chief suspect in the suicide plane attacks on New York and the Pentagon, near Washington, on Sept. 11 which killed more than 5,500 people. He is also chief suspect in the bombing of U.S. embassies in Africa and an attack on a U.S. warship in Aden last October while Clinton was still president.

Breaking a silence that he and other former presidents have imposed on themselves in the interests of national unity since the Sept. 11 attacks, Clinton said bin Laden and his followers wanted to use fear as a weapon.

"They want us to be afraid of them. They want us to be afraid of the future," Clinton said.

He warned that bin Laden's agenda included bringing down Saudi Arabia's monarchy, replacing Israel with a Palestinian state, installing regimes similar to Afghanistan's fundamentalist Taliban in Arab nations and driving the United States completely out of the Middle East.

Clinton himself had battled bin Laden. In August 1998, he ordered cruise missiles fired at bin Laden's training camps in Afghanistan and a Sudanese factory that allegedly made a precursor to chemical weapons. The strikes were ordered to retaliate for attacks in Dar es Salaam and Nairobi that left more than 200 dead.

"Make no mistake about it. This conflict represents a fundamental struggle that will go on for the next few years and will define the soul of the 21st century," Clinton said.

Clinton heartily applauded President Bush's conduct of the hunt for bin Laden, including the war he has launched against the Taliban for giving sanctuary to bin Laden and his al Qaeda network.

CLINTON TRIED TO BRING BIN LADEN TO JUSTICE

He said that his administration's best hopes of bringing bin Laden to justice were when he was expelled from Sudan. But Saudi Arabia refused to accept him and he was able to reach Afghanistan.

Once bin Laden was in Afghanistan, Clinton had high hopes that neighboring Pakistan would be able to pave the way for bin Laden's capture but Islamabad was unable to deliver.

In making his first major speech in Washington since leaving office last January, Clinton was at his best. For the first time since the attacks, it seemed, Washington felt it was all right to laugh, truly laugh.

"I never imagined I could draw a crowd like this just because my wife is a senator," Clinton said to thunderous applause from the 2,500 attendees when he walked onstage. Clinton's wife Hillary is a senator for New York while he is out of a job.

"Four more years," a lone voice at the back of the audience cried, referring to an impossible desire for him to return as president.

During his hour-long speech and a later question period chaired by his former campaign manager James Carville, Clinton, looking slimmer than when he was in the White House, was regularly interrupted by standing ovations.

Clinton said he could not promise there would not be other terror attacks but, like President Bush, urged Americans to take up their lives or the suicide bombers would have won.

Saying he had no worries about his daughter Chelsea flying, Clinton said the only place safer than a plane now was in "your own bed."

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