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Oct. 22 (Bloomberg) -- Terrorists may see the change to a new U.S. president over the next six months as a prime chance to attack, no matter who wins the White House, Homeland Security Secretary Michael Chertoff said.

``Any period of transition creates a greater vulnerability, meaning there's more likelihood of distraction,'' Chertoff said in an interview yesterday. ``You have to be concerned it will create an operational opportunity for terrorists.''

The risk is the same whether Democrat Barack Obama or Republican John McCain is elected president on Nov. 4, he said. That comment undercuts McCain's argument that the U.S. would be more in danger of an attack if Obama, 47, wins.

McCain, 72, has been citing remarks by Democratic vice presidential nominee Joe Biden on Oct. 19 that ``it will not be six months before the world tests Barack Obama like they did John Kennedy,'' should Obama win the White House.

``We don't want a president who invites testing from the world at a time when our economy is in crisis and Americans are already fighting in two wars,'' McCain said yesterday at a rally in Bensalem, Pennsylvania.

Chertoff, 54, stressed he didn't know of any specific threat to the country tied to the election or transition, and said terrorist groups are likeliest to attack when their preparations are complete.

Strike When `Ready'

``The general experience has been that they strike when they're operationally ready to strike,'' Chertoff said. The Bush administration has been making security preparations for the transition for more than 18 months, he said.

Chertoff said he was hopeful the next administration would appoint a team that would participate in a national security exercise before President George W. Bush left office.

Still, he said, he's concerned about the effect of rhetoric from some hate groups or individuals during the campaign.

``There's a general level of intemperateness in the discussion as we approach the election,'' he said. ``Do I worry that it could trigger in a disturbed individual a desire to do something? Absolutely, I worry about it.''

On March 11, 2004, an al-Qaeda cell set off 10 bombs targeting passenger trains in Madrid, killing more than 190 and injuring more than 1,400. The attack came three days before Spain's general elections.

`Logical Time'

Former CIA Director George Tenet said in his memoir that his intelligence agency went on higher alert that year, with the U.S. presidential election taking place in November. ``We believed that bin Laden has himself assessed that a logical time to attack the United States was just before the U.S. election,'' Tenet wrote.

Chertoff, who has overseen responses to hurricanes and cooperated in uncovering plots to blow up airliners during his three and a half years as Homeland Security chief, said the country is safer than it was after the Sept. 11 attacks.

He cited the nation's ports, among other areas, which are ``a hell of a lot more secure than they were seven years ago.''

Chertoff said he remained concerned about ``ungoverned space'' in Somalia, Yemen and tribal regions of Pakistan that could provide safe havens for militant organizations.

``These are spaces where terrorists can insert themselves,'' he said.

The Department of Homeland Security and other law- enforcement agencies are also monitoring cells of terrorist sympathizers already on U.S. soil, he said.

`Sleepers'

``We do have sleepers or people here who are connected back to terrorists,'' he said.

Chertoff credited administrative initiatives, such as controversial laptop searches, at the border with uncovering information about terror suspects.

``We have found on laptops things which clearly point to terrorist intent and capability,'' he said.

Chertoff said not all threats the U.S. faces are physical. As head of the administration's effort to secure the government's computer networks, Chertoff said technicians are upgrading the so-called Einstein protection system to detect and disrupt cyber attacks. Currently, the system can detect hacking only after it has occurred.

DHS is working with the private sector to strengthen security at companies such as telecommunications and energy firms that are part of the country's infrastructure, he said.

The companies aren't required to seek the government's help.

``We don't want to get ourselves into a situation where people start to feel we're imposing ourselves'' on their computer security, Chertoff said.

Illegal Immigrants

He also said his department had clamped down on illegal immigration to the point of deterring people from crossing the Mexican border.

Chertoff said the faltering U.S. economy has slowed illegal immigration, as well.

Fewer jobs also may make it more difficult for the next administration to push an immigration measure through Congress that allows temporary workers from other countries.

``My hunch is it's going to make it harder to get comprehensive immigration reform,'' said Chertoff, who led the administration's failed effort to pass legislation that included a temporary-worker program.

To contact the reporter on this story: Jeff Bliss in Washington jbliss@bloomberg.net.