New York ? The man who has led the monumental effort to put names to the remains of the World Trade Center dead has come to the sad realization that the task could end with just 2,000 victims identified.

Of the 2,823 people believed killed in the terrorist attack, 1,229 victims fewer than half have been identified, 519 by DNA alone.

Dr. Robert Shaler, the city medical examiner’s chief of forensic biology, said in an interview that the medical examiner’s office would exhaust all available forensic technology in an undertaking expected to last until the end of the year. But if the final number is 2,000, he said, “I think we’ll have done a pretty good job.”

“If we get that high,” Shaler said, hesitating, “I don’t think I’ll feel really, really glad. But I’ll feel like we’ve done the best we can do.”

Experts have said some victims probably were vaporized by the intense fires and the crushing weight of concrete and would never be identified. City officials have hesitated to venture any estimates for fear that victims’ families might interpret any number as the point where the work will stop.

For Shaler, who says he is “obsessed” with identifying the dead, the only endpoint is when all available DNA technology has been tapped.

The medical examiner’s office has become the last wisp of hope for families whose loved ones were not recovered in the trade center ruins. The recovery effort ended last month at ground zero, and on Monday the last bit of rubble will be sifted at a Staten Island landfill.

For the past 10 months, the medical examiner’s office has been conducting the biggest forensic investigation in U.S. history. Shaler manages about two dozen staffers who work full-time on trade center identifications at the facility along Manhattan’s East River. Some staffers work in laboratories extracting DNA from human remains; others analyze DNA profiles on computers.

Families regularly visit, affecting the dynamic in the laboratory as well as the scientists themselves.

“Being in this profession and being involved in a laboratory isolates you from the real world, and I think you get hardened. You steel yourself against the emotional aspects of it,” Shaler said. “That barrier has been broken down, and I’m much more emotional now.”