WASHINGTON - Former national security adviser Sandy Berger repeatedly persuaded monitors assigned to watch him review top secret documents to break the rules and leave him alone, sources said yesterday.

Berger, accused of smuggling some of the secret files out of the National Archives, got the monitors out of the high-security room by telling them he had to make sensitive phone calls.

"He was supposed to be monitored at all times but kept asking the monitor to leave so he could make private calls," a senior law enforcement source told the Daily News.

Berger also took "lots of bathroom breaks" that apparently aroused some suspicion, the source added.

It is standard security procedure to constantly monitor anyone with a security clearance who examines the type of code-word classified files stored in the underground archives vault in the building where tourists view the Declaration of Independence and the Constitution.

Asked if guards left Berger alone in the classified reading room while he made calls, archives spokeswoman Susan Cooper replied, "I'm not going to say I haven't heard that."

The same archives monitors told the FBI that Berger was observed stuffing his socks with handwritten notes about files he reviewed that were going to the 9/11 panel. It is prohibited to make notes about the secret files and leave with them without special approval.

"Stuffed socks and pockets is real," the senior law enforcement official said. "The [theft] was reported by the guards."

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Even though the Justice Department launched the investigation last year, the Republican-controlled House Government Reform Committee began its own inquiry yesterday.

The government source said the Archives employees were deferential toward Berger, given his prominence, but were worried when he returned to view more documents on Oct. 2. They devised a coding system and marked the documents they knew Berger was interested in canvassing, and watched him carefully. They knew he was interested in all the versions of the millennium review, some of which bore handwritten notes from Clinton-era officials who had reviewed them. At one point an Archives employee even handed Berger a coded draft and asked whether he was sure he had seen it.

At the end of the day, Archives employees determined that that draft and all four or five other versions of the millennium memo had disappeared from the files, this source said.

This source and another government official said that archivists gave Berger use of a special room for reviewing the documents. He was examining the documents to recommend to the Bush administration which papers should be released to the commission investigating the Sept. 11, 2001, attacks. Archives spokeswoman Susan Cooper said that employees closely monitor anyone cleared to review classified presidential materials.

The contradictions over basic facts, such as when Berger was first alerted to missing documents, have characterized the controversy this week.

The controversy is likely to continue, even after Berger relinquished his role as informal Kerry adviser on Tuesday. House Government Reform Committee Chairman Thomas M. Davis III (R-Va.) said yesterday that he plans an investigation.

"These allegations are deeply troubling, and it's our constitutional responsibility to find out what happened and why," Davis said in a statement. "It boggles the mind to imagine how a former national security advisor walked off with this kind of material in his pants, or wherever on his body he carried it. At best, we're looking at tremendously irresponsible handling of highly classified information -- some of which, I understand, has not yet been located."

The documents Berger took — each copy of the millennium report is said to be in the range of 15 to 30 pages — were highly secret. They were classified at what is known as the "code word" level, which is the government's highest tier of secrecy. Any person who is authorized to remove such documents from a special secure room is required to do so in a locked case that is handcuffed to his or her wrist.

It is not clear why Berger would focus solely on the millennium-plot report. But it is clear that the report has been the object of intense discussions during the September 11 investigation.

The report was the result of a review done by Richard Clarke, then the White House counterterrorism chief, of efforts by the Clinton administration to stop terrorist plots at the turn of the year 2000. At several points in the September 11 commission hearings, Democrats pointed to the millennium case as an example of how a proper counterterrorism program should be run. But sources say the report suggests just the opposite. Clarke apparently concluded that the millennium plot was foiled by luck — a border agent in Washington State who happened to notice a nervous, sweating man who turned out to have explosives in his car — and not by the Clinton administration's savvy anti-terrorism work. The report also contains a number of recommendations to lessen the nation's vulnerability to terrorism, but few were actually implemented.

The after-action review became the topic of public discussion in April when Attorney General John Ashcroft mentioned it in his public testimony before the September 11 commission. "This millennium after-action review declares that the United States barely missed major terrorist attacks in 1999 and cites luck as playing a major role," Ashcroft testified. "It is clear from the review that actions taken in the millennium period should not be the operating model for the U.S. government."

In May, a government official told National Review Online that the report contains a "scathing indictment of the last administration's actions." The source said the report portrayed the Clinton administration's actions as "exactly how things shouldn't be run." In addition, Clarke was highly critical of the handling of the millennium plot in his book, Against All Enemies.

It is not clear how many copies of the report exist. Nor is it clear why Berger was so focused on the document. If he simply wanted a copy, it seems that taking just one would have been sufficient. But it also seems that Berger should have known that he could not round up all the known copies of the document, since there were apparently other copies in other secure places. Whatever the case, the report was ultimately given to the September 11 Commission.