The Department of Homeland Security was created after 9/11 to be our domestic security blanket, but its newly sworn-in chief, Michael Chertoff, will have to mend some gaping holes in the fabric before he can move on to new challenges.

Chertoff's government experience, and particularly his recent efforts to promote information-sharing within the FBI, makes him ideally suited to the task of forging coordination and cooperation within his new realm. The DHS is a sprawling amalgam of 22 agencies that have yet to be molded into a functioning whole.

His ultimate success, though, will depend not only on the flow of information but also on its quality. Right now, much of that information is sequestered in the brains of a far-flung cadre of experts working to apply engineering and technology advances to homeland defense.

In more than a year of interviews with scores of such front-line defenders, we've gleaned a range of tactical insights into our greatest vulnerabilities in the quest to make Americans safer:

* A symbolic first step, but an important one, will be for Chertoff to revise the much-maligned color-coded alert system (sometimes referred to as the "rainbow of doom") into something useful.

Chertoff is our communications director in periods of crisis, but government communications lag far behind those of CNN, not to mention the bloggers, text-messagers and spammers. Chertoff has an up-and-running infrastructure at his fingertips, but he needs to win public confidence that he knows how to deploy it.

* A nuclear weapon hidden inside a shipping container is the gravest danger facing this country. Chertoff needs to expand programs to post inspectors in foreign ports and accelerate the funding of research into "smart" containers, which can be monitored with sensors and tracked using radio-frequency ID tags. Customs inspectors don't have the resources or time to search more than a small fraction of the roughly 7 million containers entering the country each year. Computer profiling of containers is essential.

* The new secretary needs to cultivate an appreciation of on-the- ground emergency response. No one in Washington likes to admit that homeland security involves confronting the consequences of attacks we've failed to prevent, but this is a harsh reality. Chertoff must address the concerns of thousands of fire departments and rescue services across the nation, emphasizing the development of better communications equipment and response strategies for the urban areas deemed most at risk for terrorist events. Many of these feet-on-the- street warriors felt overlooked during Tom Ridge's tenure as secretary.

* Chertoff must also confront the potential cascade effects of a successful terrorist attack. Beyond the individual city (or port or chemical plant) affected lies the landscape of secondary effects: the shortages of goods and services, the transportation shutdowns and the electrical outages that can spell long-term social and economic disaster. Chertoff needs to push industry to build in backup systems and redundancies. He should enlist the expertise of engineers, such as those at the Sandia National Laboratory, who know how to assess the viability of our networks, from food delivery to water supply.

* Chertoff needs to focus on securing more public funding for bioterrorism initiatives, emphasizing the kind of basic biological research that has application beyond one or two exotic germs. As became clear during this recent flu season, effective protection against natural -- much less deliberate -- disease outbreaks is sorely lacking, and pharmaceutical companies have very little incentive to invest in new vaccine and antibiotic development.

* Almost 3 1/2 years after 9/11, the government has made only spotty progress in securing air travel, the greatest source of daily anxiety to a mobile public and, according to David Stone, the new Transportation Security Administration chief, the arena still at greatest risk of terrorist attack. The TSA has yet to institute a computerized passenger-screening system to replace the one in use on 9/11. The last upgrade was scrapped due to ineffectiveness and privacy concerns. And Secure Flight, the current contender, won't be rolled out until August. Even if it can assuage public concern about its invasiveness, Secure Flight can only help flag suspicious passengers so that human screeners can then step in. Chertoff should push the TSA to enhance training.

The DHS is far from the nimble, integrated agency it needs to be. But Chertoff has 180,000 staffers awaiting new direction, as well as a gathering force of technologists, scientists, emergency workers and others prepared to work with him and each other. And he has all of us -- citizens of the Information Age, whose eyes, ears and energies can be a potent force. For all our sakes, he needs to swiftly connect the parts of this homeland security network.

Credit: Martha Baer, Evan Ratliff and Katrina Heron are co-authors of "SAFE: The Race to Protect Ourselves in a Newly Dangerous World" (HarperCollins, 2005).