Even as the federal government is attempting to learn its lessons and correct its many tragic mistakes in the aftermath of Hurricane Katrina, it stubbornly insists on endangering a segment of those affected by the storm, undermining its own relief effort and that of private agencies. For some of the storm's victims, it seems, even our shelters are not a safe harbor.

For the first time in decades, federal officials refused to make the announcement that they have always made after a disaster. Every recent administration, including this one after the Sept. 11 attacks, has announced for humanitarian reasons as well as for the success of the government's rescue operation that immigration authorities will not use the relief effort as an enforcement opportunity. Indeed, Homeland Security Secretary Michael Chertoff was quick to announce that his agency would not engage in enforcement against employers of immigrants.

But the customary announcement regarding immigrants themselves never came. Even as White House officials were assuring community leaders and the ethnic media that they wanted all of the storm's victims to seek help, DHS officials were refusing to provide the necessary assurances that it was safe to come forward, leaving my organization, the National Council of La Raza, and our allies with a dilemma: Do we encourage people to seek help knowing that the government might use it against the very people we are trying to reach? Refusing to give assurances is one thing, but would the government really spend its enforcement resources on hurricane victims?

Apparently, the answer is yes. The Wall Street Journal reported early this month that "police and the U.S. Marshals Service swept into a Red Cross shelter for hurricane refugees [in Long Beach, Miss.]. They blocked the parking lot and exits and demanded identification from about 60 people who looked Hispanic, including some pulled out of the shower and bathroom, according to witnesses."

The only people in the shelter subjected to this treatment were Latinos, including those born in the United States who were there to help; at least one shelter manager, a former Marine and a Vietnam veteran who happened to be Hispanic, was also temporarily detained and screened. This follows several reports of immigrants being placed in deportation proceedings immediately after being taken to safety by government authorities in Texas and West Virginia.

No matter what you believe about the nation's failed immigration policies and the presence of undocumented immigrants in the United States, you should be alarmed that the federal government is willing to breach the promise of safe harbor offered by its own agencies and those run by private charities. Not only does it offend every basic humanitarian principle to round up those who have sought help out of desperation, but it does grave damage to the larger public health and safety.

The success of disaster preparedness and relief depends on the ability to reach everyone who is at risk, to urge them to seek shelter, medical care and other lifesaving services. If there were an outbreak of communicable disease in Katrina's wake -- which is not unthinkable under the circumstances -- the last thing you want to do is convince a segment of the nation's largest minority that the government is not a safe source of preventive care and treatment. If, God forbid, the next crisis involves a biological weapon or an influenza outbreak, the government has just undermined its ability to keep us all safe. Lives are on the line, and not just the lives of the immigrants we too often find expendable.

The writer is president and chief executive of the National Council of La Raza, the Latino civil rights and advocacy organization.