The Justice Department has ordered Random House, which published former CIA official Frank Snepp's "Decent interval," to disclose all its documents concerning that account of the fall of South Vietnam.

The Justice Department is suing Snepp for all the money he has earned from his book on the grounds that his gains are "unjust enrichment" because Snepp signed a pledge demanded of all CIA officers when he joined the agency to submit any manuscript to it for prepublication approval.

The suit is the first full test of the constitutionality of that pledge.

Attorney General Griffin B. Bell told a news conference two months ago: "If that contract isn't valid, we and everyone ought to know it. If it's valid, it ought to be enforced."

Snepp has said he decided not to submit his book before publication because it contains no classified information and because government officials had been leaking self-serving versions of events surrounding the collapse of South Vietnam to the press.

The subpoenas delivered to Random House ordered the publishing house's chief, Robert L. Bernstein, and Snepp's editor, Robert Loomis, to appear at the New York U.S. attorney's office next week, and to bring with them, in effect, all documents concerning their relations with Snepp and his book.

A spokesman for Random House said yesterday that the subpoenas would be honored and Random House was in the process of gathering the documents.

The government specifically ordered Random House to produce all documents "which related to, discuss or mention the decision or conclusion, explicit or implicit, not to submit ["Decent Interval"] to the CIA for agency reveiw prior to publication of the book."

It also calls for all documents concerning monies earned by the book or by the sale of any form of republication rights.

On March 31, U.S. District Court Judge Oren Lewis in Alexandria refused a Justice Department request for an immediate ruling against Snepp and gave both sides two months together evidence in the case.

The Justice Department argued that the case follows the precedent of a book of former CIA officer Victor Marchetti and John Marks, "The CIA and the Cult of Intelligence."

The 4th U.S. Circuit Court of Appeals ruled that Marchetti's contract signed when he joined the CIA was valid, but applied only to any classified information he sought to publish.

The CIA won the right to delete passages from the Marchetti manuscript.

Snepp's attorney argued that since "Decent Interval" contains no classified material, the case if different from marchetti's.

"Decent Interval" accuses the U.S. government of bungling the final evacuation from Saigon and thereby leaving behind thousands of Vietnamese who had worked for the CIA and model U.S. agencies.