WASHINGTON - China is refusing to take back an estimated 39,000 citizens who have been denied immigration to the United States and have clogged detention centers at federal expense, Homeland Security Secretary Michael Chertoff said Tuesday.

In an interview with The Associated Press, Chertoff said that China last year readmitted 800 people. But that made only a small dent in what he described as a backlog of thousands illegally in the U.S.

"The math is pretty easy ¡ª at that rate, we wind up with increasing numbers of migrants who, if we're going to detain them, we're going to have to house at enormous expense," Chertoff said.

He added: "We can't be in the position any longer where we are paying the burden and bearing the burden for countries that won't cooperate with us and take their own citizens back."

The Chinese Embassy in Washington did not immediately return a call for comment.

Currently, 687 Chinese are being held in federal detention facilities, at a daily rate of $95 each, while some 38,000 have been released on bond or under a monitoring program, such as wearing an electronic surveillance bracelet, the Homeland Security Department said later Tuesday.

Illegal immigrants can be held for 180 days before they are released.

Chertoff also said Homeland Security would open detention facilities in the next few weeks to house entire families of illegal immigrants who hope to bring their children along in order to avoid jail time. "It'll be humane, but we're not going to let people get away with this," he said.

Chertoff's remarks comes as the Homeland Security Department aims to end its "catch and release" immigration policy by Oct. 1. After that date, all illegal immigrants will be held in U.S. detention centers until they can be returned to their nation of citizenry.

Over the last five years, Homeland Security has deported more than 2,580 Chinese nationals, department data show. Though other nations also are refusing to take back citizens who have been denied U.S. immigration, Chertoff refused to name them Tuesday, noting that the number of stranded citizens from China far outpace those from other counties.

Chertoff visits China, Japan and Singapore at the month's end. He said financial decisions and a cumbersome process may contribute to China's reluctance to take back its citizens, but also "I think sometimes maybe it's a low priority."

"But they've got to understand it's a high priority for us," he said.

Speaking earlier to the National League of Cities, Chertoff made a veiled reference to recent criticism aimed at him for his department's inadequate response to Hurricane Katrina. Though some lawmakers have called on Chertoff to resign, or said he should be fired, the White House has repeatedly maintained its support for him.

"People used to say to me, 'Why would you want to give up a lifetime job in order to take this job?'" said Chertoff, who was a federal appeals court judge until he was confirmed last year as the nation's second homeland security chief. "And I didn't realize until a couple weeks ago that really, every year in this job is a lifetime. So in that sense, maybe I've traded up."