The Justice Department has told an appellate court here that the government is required by law to maintain the integrity of President Richard M. Nixon’s White House tapes and that it has no obligation to cut out portions of them to satisfy the demands of Nixon’s estate.

A federal court here has ordered the National Archives to return all “personal or private conversations” on the original tapes to the late president’s estate “forthwith.” In an appeal brief filed late last Wednesday, however, lawyers at Justice said this would jeopardize “virtually all” of the 950 reels of tape from the Nixon presidency that Congress confiscated by law in 1974 to keep Nixon from destroying them.

The stated purpose of the bill that became the Presidential Recordings and Materials Preservation Act of 1974, the 44-page brief said, was “to protect and preserve tape recordings involving former President Richard M. Nixon and made during his tenure.” A provision of the law explicitly directs the archivist of the United States to protect the recordings “from loss or destruction.”

At issue are 820 hours of private or personal conversations scattered throughout the 4,000 hours recorded on Nixon’s sound-activated taping system from 1971 to 1973, when the setup was disclosed during Senate hearings on the Watergate scandals.

Nixon lawyers contend the private portions of the originals must be returned to them under a section of the 1974 law calling for adoption of regulations providing for public access to the tapes but respecting “the need” to give Nixon or his heirs “sole custody and use” of the personal segments.

Citing government experts who said the originals are too fragile to be cut up without permanent damage, the Justice lawyers said the “sole custody” exception applies only to the rules for public access and does not override the duty imposed on the archivist to protect the originals.

The 1974 law also states that none of the tapes shall be destroyed “except as hereafter may be provided by law.” But the brief maintained that Congress was talking about a future law, and “no such later law” was ever enacted. Nixon’s privacy interests, the brief said, will be preserved because the original tapes will be kept intact in a special vault, without any provision for public access.

A hearing is scheduled for late February. Nixon lawyers contend that the originals can be safely spliced and that, in any case, the Archives will retain enhanced copies that can be safely edited “without the loss of a single second of the nonprivate conversations.”