DES MOINES, Iowa - The assassination of Benazir Bhutto in Pakistan jolted the race for the White House yesterday, sending candidates in both parties scrambling for political advantage while condemning the attack.

Republican Sen. John McCain of Arizona and Democratic Sen. Hillary Rodham Clinton of New York, who have made experience a cornerstone of their campaigns, said that the murder was proof of a need for a president who is ready to take command.

"I know from my lifetime of experience, you have to be prepared for whatever might happen, and that's particularly true today," Clinton said while campaigning in Iowa.

Said McCain: "My theme has been throughout this campaign that I'm the one with the experience, the knowledge and the judgment. So perhaps it may serve to enhance those credentials to make people understand that I've been to Pakistan; I know Musharraf. I can pick up the phone and call him. I knew Benazir Bhutto."

Asked later by reporters about his rivals, McCain said former Arkansas Gov. Mike Huckabee doesn't have "the same experience and background on national security issues that I do."

He said that former New York Mayor Rudy Giuliani had done a great job with a "post-crisis situation" after terrorists brought down the World Trade Center towers on Sept. 11, 2001.

"I'm not saying he is without credentials," McCain added. "I'm saying I am the one with the most credentials and the most experience and the most judgment."

Giuliani issued a statement that said the assassination was further evidence that the United States needs to increase its efforts against terrorism, and he began running an a new TV ad focusing on the 9/11 attacks.

Mitt Romney was eager to join the debate.

"If the answer for leading the country is someone that has a lot of foreign-policy experience, we can just go down to the State Department and pick up any one of the tens of thousands of people who spent all their life in foreign policy," he said while campaigning in New Hampshire.

Instead, he said, what is needed is a chief executive with leadership and the ability to assemble "a great team of people."

The assassination of Bhutto provided a reminder of the importance of national security in an era of terrorism.

Some recent public-opinion polls have shown more people expressing concern about the economy than events overseas.

In Iowa, officials disclosed that internal polling by the top three Democratic campaigns showed Clinton, Sen. Barak Obama and former North Carolina Sen. John Edwards in a virtual dead-heat.

Among Republicans, private and public polls in Iowa show Huckabee with the lead over Romney, who had been the front-runner in the state for months. In New Hampshire, site of a primary five days after Iowa votes, Romney polls narrowly ahead of McCain, who has made gains in recent weeks as Giuliani and former Tennessee Sen. Fred Thompson have faded.

Alone among the White House contenders, New Mexico Gov. Bill Richardson called on President Bush to pressure Pakistani President Pervez Musharraf to step aside in favor of a coalition government.

"Until this happens, we should suspend military aid to the Pakistani government," he said in a statement. "Free and fair elections must also be held as soon as possible," added Richardson, who served as ambassador to the United Nations for a portion of the Clinton administration.

Obama said he had asked the administration for intelligence briefings on a dicey situation.

In a criticism of current policy, he said the war in Iraq had diverted troops and other resources needed to track down al Qaeda terrorists who move between Afghanistan and Pakistan. "I've been saying for some time that we've got a very big problem there," Obama. said.

Edwards said he had talked with the Pakistani president, and urged him to "continue on the path to democratization, to allow international investigators to come in to determine what happened."

Said Huckabee: "The terrible violence surrounding Pakistan's upcoming election stands in stark contrast to the peaceful transition of power that we embrace in our country through our Constitution. On this sad day, we are reminded that while our democracy has flaws, it stands as a shining beacon of hope for nations and people around the world who seek peace and opportunity through self-government."

Sen. Joseph Biden, D-Del., chairman of the Senate Foreign Relations Committee, told reporters in Iowa that he had twice this past fall urged Musharraf "to provide better security for Ms. Bhutto and other political leaders. . . . The failure to protect Ms. Bhutto raises a lot of hard questions for the government and security services that must be answered." *