Six months after the World Trade Center attack, 158 people are officially classified as missing — some of them almost certainly dead, some perhaps mistakenly on the list, and some possibly trying to fake their deaths.

The missing include firefighters and foreign visitors, bond brokers and illegal immigrants working mostly food-service and maintenance jobs, an analysis has found.

In many cases, families have mourned these people and their employers consider them dead, but their remains have not been identified and no one has applied for a death certificate. Some are illegal immigrants whose families, often living in other countries, have been unable to obtain death certificates because the victims' employers will not cooperate.

Others may not be dead at all — they were wrongly reported missing in the chaos after Sept. 11 or may be trying to fake their deaths, according to police.

The Police Department estimates at least 60 percent of the 158 still classified as missing did die in the attack, while the rest require further investigation.

The official city count of the missing and dead peaked at 6,729 on Sept. 24 but quickly began dropping as the list was cross-checked for mistakes and duplicated names.

City officials say 2,672 people are confirmed dead, either by identified remains or a death certificate issued by a court based on proof that the victim was in the trade center at the time of the catastrophe.

The remaining 158 were reported missing by family and friends, but so far, nothing officially proves they died on Sept. 11. While the city would not provide the names of the missing, officials agreed to speak in broad terms about the list. An Associated Press database of people reported missing, and a list posted by the city medical examiner in January, were also analyzed.

Firefighter Michael Kiefer and two others from Engine 132 in Brooklyn are among those still officially listed as missing, even though there is little doubt they died.

Kiefer's family has chosen not to apply for a death certificate and will not hold a memorial service until his remains are found, said his father, Bud Kiefer.

"Having him missing and having the circumstances surrounding it is one of the most horrible things you can go through," Kiefer said. "Having a piece of paper confirming something like that could be 10 times worse."

Kiefer said his son was a devout Roman Catholic and would have wanted the family to postpone services until his remains were identified. He added that the usual reasons for obtaining death certificates — to obtain life insurance, process wills and access bank accounts — were not pressing matters for his family.

Some families of illegal immigrants lost in the trade center are desperate to get death certificates but are finding that employers will not sign affidavits confirming their loved ones worked there.

Employers are afraid to admit they were paying the workers illegally, according to Joel Magallan, executive director of the Tepeyac Association of New York, an immigrant rights group.

"Those people who were undocumented, they were not on the payroll and were paid by cash," Magallan said.

The issue of illegal immigrants is just one of many that foreign consulates have faced as they work with city officials to untangle the missing-person reports.

Five people on the Greek consulate's missing list have been impossible to find, said Dimitris Gemelos, a spokesman for the consulate.

"These people could still be alive," he said. "We certainly have tried to reach these people and their families, but we have had no word."

Dozens of consulates, along with police in New York, have done the same, spending months dealing with misspellings, wrong telephone numbers and piecemeal information.