There has been commuter chaos in parts of Australia's biggest city, a result of the tightest security the country has ever seen. The disruption to daily life, caused by this week's Asia-Pacific Economic Cooperation summit, has been so massive that President Bush has apologized to the people of Sydney for the inconvenience caused by his visit. Phil Mercer files this report from Sydney.

The visit of President Bush and other world leaders has prompted Australian authorities to mount an unprecedented security operation.

Five thousand police officers and troops are on patrol, along with fighter jets and combat helicopters.

In the center of Sydney, a giant steel barrier has been erected to protect key APEC summit sites. Parts of downtown Sydney have been declared no-go zones for the public.

The sweeping measures have caused peak-hour chaos, with angry commuters being met by a raft of road closures. Many residents have asked why the conference was not held in the national capital, Canberra, which has hosted many high-profile visits in the past.

The already tight clampdown has been increased since the arrival of President Bush late Tuesday.

On Wednesday, Mr. Bush told the people of the city he is sorry to be responsible for so much disruption.

"Look, I don't want to come to a community and say, you know, what a pain it is to have the American president. You know, unfortunately, however, this is what the authorities thought was necessary to protect people, and uh, we live in a free, you live in a free society, people feel like they want to protest, fine, they can," said Mr. Bush. "And unfortunately, evidently, some people may want to try to be violent in their protest. But I apologize to the Australian people if I've caused this inconvenience."

Thousands of people are expected to take part in rallies to voice their feelings on a range of issues, from the Iraq war to the environment. They are also demonstrating over a number of domestic issues, including unpopular labor reforms.

Activists have insisted they want to make their point peacefully, but there has been violence at other international gatherings in recent years, and the police are prepared for that eventuality here. The Sydney authorities have cleared out jail cells to be prepared for any mass arrests of protesters.

Even without the protests, such hot issues as climate change and Iraq are expected to be key themes during a week of meetings among APEC officials. The meetings will culminate in the leaders' summit at the end of the week.

The Asia-Pacific Economic Cooperation forum is a loose grouping of economies that border the Pacific Ocean. Its 21 members include the United States, China and Japan, and smaller economies in the Asia-Pacific and Latin America.