Lawyers representing Richard Nixon's estate have not clearly defined the differences among informational, evidentiary and artifactual value in regard to possible sale of his records. Yet what is valuable to a historian differs from what is valuable to a collector.

Mr. Nixon would have faced enormous encumbrances in preparing historical information for sale in 1974. He would have had to screen 3,700 hours of tapes to ensure he did not disclose classified or slanderous information. Given the surreptitious nature of his recordings, he might not have been able to sell the tapes without obtaining permission from the people he had taped.

According to the Nixon lawyers, historians most value information about the Vietnam War and foreign policy--precisely the type of information that must be screened for national security before disclosure. Mr. Nixon's National Security Council files, for example, have yet to be released by the National Archives.

The Nixon lawyers contend that the former president could have hired private citizens to segregate classified from unclassified information, but the Justice Department says that this is "contrary to government policy and practice" and that "a more preposterous, unlawful scenario cannot be imagined."

Government archivists screen everything, even constituent letters, for personal privacy, Social Security numbers, etc. But Mr. Nixon perceived other encumbrances when he blocked the National Archives from opening 42,191 unclassified documents in 1987. Because of Mr. Nixon's intervention, historian Stephen Ambrose lacked access to these documents when he published a three-volume Nixon biography between 1987 and 1991.

Although federal archivists deemed the documents releasable, Mr. Nixon fought so tenaciously to keep them secret that the National Archives did not open most of them until after he died in 1994. Some of the documents he blocked in 1987 included his comments about ethnic groups and government employees, Vietnam and Watergate.

While Mr. Nixon and the government have differed on what to disclose from his tapes and files, it is clear both viewed his records as so encumbered that a document dump in 1974 would have been impossible.

MAARJA KRUSTEN

Arlington

The writer is a former National Archives Nixon tapes archivist.