The fourth anniversary of the Sept. 11, 2001, terrorist attacks is days away. There are repeated attacks in London. Egyptian resort hotels are being blown apart. The New York Police Department is checking bags on the subway. Are we any safer?

It's a loaded question. More than a dozen security experts, such as Tom O'Brien, a retired customs agent who co-founded Global Trade Security Consulting, and Dr. Marshall Moore, a U.S. Navy physician and Bioweapon Attack First Responder specialist, agree the U.S. is safer, but see another attack as a matter of when, not if.

Defending the American citizenry is the Department of Homeland Security, created in November 2002 in the biggest government reorganization since 1947.

But the DHS, which has 180,000 employees and a proposed fiscal 2006 budget topping $41 billion, "has a near impossible task," says Richard Wilmot, a retired brigadier general in the U.S. Army and now a security consultant. "The terrorist has every advantage. We can't protect everything, 9/11 is all but forgotten and we have weak spots. We have to assume something will happen again and ask what are the really weak spots to be targeted. It's easy to talk about but hard to do."

To prevent a second major attack, Homeland Security Secretary Michael Chertoff, only on the job since February, unveiled on July 13 his "second stage review," a plan to overhaul the department's bureaucracy.

Among other tacks, Chertoff created a Chief Medical Officer position to be a single point of contact in the event of a bioterror attack. He also established the post of assistant secretary for the private sector to deal with industry, which holds 85% of the country's physical infrastructure, including especially vulnerable targets such as chemical plants and nuclear facilities. He also elevated the position of cybersecurity in the department, making the defense of the Internet and telecommunications equivalent to defending roads and bridges.

"Much work has been done," said Chertoff on July 13. "Much remains to do."

Although issues facing the DHS are huge, they aren't vastly different from what corporate executives face, according to Wilmot.

How well is the government doing to protect the U.S.? Check out our: Homeland Security Report Card

The agency has to streamline internal processes and procedures, and break down what Wilmot calls separate "sandboxes," or divisions. The DHS also has to integrate its operations with a vast number of partners—states, local municipalities and the companies that do everything from distribute milk to manufacture vaccines. And like any large organization, Homeland Security needs to work closely with international intelligence agents and security officials.

Here's a look at the department's main hurdles.

Challenge: Combining 22 separate agencies into one efficient unit.

Solution: Picking priorities based on risk and returns.

Progress: Slow. More organizational changes ahead.

Chertoff's plan revolves around analyzing risks. Think of it as return on investment, where the return is saved lives and the variables are threats, vulnerability and consequences. Bottom line: A chemical weapon in a subway system gets priority over a bomb in a subway car. This analysis is necessary to make "tough choices about how to invest finite human and financial capital," Chertoff says.

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To Chertoff, securing mass transit has to be different from, say, protecting a federally controlled airport where people enter and depart at fixed points. A mass transit system is governed by local municipalities, has huge numbers of embarking and debarking points on streets, and thus is harder to defend.