"I owe the president ... a great apology that this may have caused him and his administration a big distraction," Bernard Kerik said in a telephone interview with The Associated Press.
"I'm going to spend some time with my family. I'm going to work on getting messages out to people close to me who have been supportive, apologizing for the embarrassment," Kerik said.
Speaking from his home in Franklin Lakes, N.J., the 49-year-old Kerik said he had discovered a few days ago that he did not pay all required taxes for a family nanny-housekeeper and that the woman may have been in the country illegally.
The surprise withdrawal by the former New York City police commissioner sent Mr. Bush back in search of a nominee to head the sprawling Homeland Security Department, which was created after Sept. 11, 2001, to improve coordination and protection against future terrorist attacks.
On Saturday, former New York mayor Rudy Giuliani, who has been mentioned as a possible choice, expressed no interest in the job. "I am not a candidate," he told reporters in New York.
Sen. Susan Collins, the Maine Republican who heads the Senate committee that will take up the nomination, said two "terrific choices" would be Asa Hutchinson, the department's undersecretary for border and transportation security, and Sen. Joe Lieberman, D-Conn.
Among the names that had been circulating for the post before Kerik's selection on Dec. 3 were Joe Allbaugh, former director of the Federal Emergency Management Agency; Mike Leavitt, former Utah governor and now head of the Environmental Protection Agency; and White House homeland security adviser Fran Townsend.
But it was still possible that the White House would break the search wide open again rather than return to the previous stable of top contenders, said a senior administration official, speaking on condition of anonymity.
"We will certainly work to name someone as quickly as possible," White House spokeswoman Claire Buchan said Saturday.
Meanwhile, questions continued over how the White House review process could have missed the kind of "nanny problem" that scuttled high-level appointments in both the Clinton administration and the first Bush administration.
"There's a standard vetting process that we go through with all nominees and certainly we did that" with Kerik, Buchan said. She said it was solely Kerik's decision to withdraw late Friday.
Mr. Bush, leaving a Maryland hospital afterSaturday, ignored a question about Kerik's withdrawal.
Giuliani, a close friend of Kerik's, said Bush administration officials asked Kerik from the beginning whether there were any issues involving domestic employees.
"He didn't think he had a problem," Giuliani. "He made a mistake."
Giuliani said he was "heartbroken" by the withdrawal, but that Kerik had no other choice. "The irony of this is he's about as qualified as you could possibly be for this job."
CBS News Correspondent Mark Knoller says, "Despite the nanny problem, if Kerik was willing to continue through the confirmation process, the White House was willing to stand by him.
"A senior official tells CBS News that Mr. Bush thought Kerik was the right man for the job, and still does, though he must now seek another nominee. It was the White House vetting process that failed to uncover the nanny problem, the official says."
Kerik's personal lawyer, Joseph Tacopina, said it was Kerik's call to withdraw. "It was Bernie Kerik who uncovered this on his own. He brought it to the White House," said Tacopina, who described Kerik as "distraught."
Bush advisers, now having to deal with the kind of messy situation they had so far avoided, were taking Kerik at his word that he had not intentionally misled them, the official said.
Because the issue involved immigration — and the Homeland Security Department includes the immigration agency — Kerik had no choice but to withdraw, Giuliani said. "Every time immigration issues came up this would be a problem."
"It would have been a bitter, difficult battle that probably would have ended without him getting confirmed," Giuliani said.
In the AP interview, Kerik said that on Wednesday — five days after Bush announced his selection — he discovered financial records "that led me to question" whether proper taxes had been paid for the housekeeper. By Friday, he said, "I came to realize ... there may have been a question with regard to her legal status in the country."
Since his nomination was announced, other issues have surfaced indicting that Kerik's confirmation by the Senate might not have gone smoothly.
Some lawmakers have questioned whether Kerik had the management experience to oversee the department, which has 180,000 employees.
Democrats also focused on potential conflict of interest issues because of Kerik's recent $6.2 million windfall from exercising stock options in a stun gun company that does business with the federal department.
According to a report in Newsweek, Kerik also was involved in a civil dispute six years ago after he failed to pay maintenance fees on a New Jersey condominium he owned. At one point an arrest warrant was issued, the magazine said.
Kerik on Saturday denied an arrest warrant was ever issued, but said he had been ordered to appear at a foreclosure hearing. "The lawsuit was settled, the apartment was not foreclosed on," he added.