Questions about the archives’ capacity have added a new element to the uneasiness felt by open-government advocates and historians, who already fear that departing White House officials, particularly Vice President Dick Cheney, may not turn over everything. Mr. Cheney asserted this month in a court case that he had absolute discretion to decide which of his records are official and which are personal, and thus do not have to be transferred to the archives,

The National Archives has already begun trucking boxes of paper records from the White House to a warehouse it is leasing in Lewisville, Tex., not a great distance from where Mr. Bush’s presidential library is to be built, at Southern Methodist University in Dallas.

The archives invoked its emergency plan to deal with problems in transferring two types of electronic files: a huge collection of digital photographs and the “records management system,” which provides an index to most of the textual records generated by Mr. Bush and his staff members in the last eight years.

Archivists said it could be weeks or months before these files could be indexed and searched.

In their plan, archives officials wrote, the transition poses “unique challenges” because of the huge volume of electronic records, some of them in “formats not previously dealt with.” Even though archivists have been working with the White House to survey the documents, “there is always a possibility that some electronic records may be overlooked,” the officials wrote.

If the electronic records of the Bush White House total 100 terabytes of information, as archives officials estimate, that would be about 50 times the volume of electronic records left behind by the Clinton White House in 2001 and some five times the contents of all 20 million catalogued books in the Library of Congress.