The administration agreed last year to produce all responsive records about the visits "without redactions or claims of exemption," according to a court order.
But in a court filing Friday night, administration lawyers said that sometime in the past year the Secret Service identified a category of highly sensitive documents that might contain information sought in a lawsuit about Abramoff's trips to the White House.
The Justice Department declared that the contents of the "Sensitive Security Records" cannot be publicly revealed even though they could show whether Abramoff made more visits to the White House than those already acknowledged.
"The simple act of doing so ... would reveal sensitive information about the methods used by the Secret Service to carry out its protective function," the Justice Department argued.
Sensitive Security Records are created in the course of conducting more extensive background checks on certain visitors to the White House. In sworn statements accompanying the filing, two Secret Service officers said the extra attention is paid to some visitors because of the background, "the circumstances of the visits," or both.
The Justice Department said that releasing the information could allow people to figure out the protective activities of the Secret Service.
The filing came in a lawsuit by a conservative watchdog group, Judicial Watch. Another private group, Citizens for Responsibility and Ethics in Washington, also has requested Secret Service records of Abramoff's White House visits, and on Friday, the Justice Department asked that the two suits be consolidated.
To date, the government has turned over Secret Service records referring to seven White House visits by Abramoff - six of them in the early months of the Bush administration in 2001, and the seventh in early 2004, just before Abramoff came under criminal investigation.
The White House has released little information about the visits, but none of them appears to involve a small group meeting with President Bush.
"This is an extraordinary development and it raises the specter that there were additional contacts with President Bush or other high White House officials that have yet to be disclosed," said Tom Fitton, president of Judicial Watch. "We've alleged that the government has committed misconduct in this litigation and frankly this is more fuel for that fire."
The White House had no immediate comment Saturday.
Nearly two years ago, just after Abramoff had pleaded guilty in the influence peddling scandal, Mr. Bush told reporters, "I can't say I didn't ever meet" Abramoff, "but I meet a lot of people."
"I don't know him," Mr. Bush said at the presidential news conference in January 2006. "I've never sat down with him and had a discussion with the guy."
After the president's comments, Abramoff wrote an e-mail to the national editor of Washingtonian magazine saying that Mr. Bush had seen him "in almost a dozen settings, and joked with me about a bunch of things, including details of my kids. Perhaps he has forgotten everything, who knows."
Time magazine reported that its reporters had been shown five photographs of Mr. Bush and Abramoff. Most of them, the magazine said, had "the formal look of photos taken at presidential receptions."
The Justice Department probe of Abramoff and his team of lobbyists has led to convictions of a dozen people, including former Rep. Bob Ney, R-Ohio, former White House official David Safavian and former Deputy Interior Secretary Steven Griles.
Abramoff is serving six years in prison on a criminal case out of Florida. He has not yet been sentenced on charges of mail fraud, conspiracy and tax evasion stemming from the influence-peddling scandal in Washington.
By Pete Yost