The coding information that retired Navy communications specialist Jerry Alfred Whitworth allegedly passed to the Soviet Union is "probably the most sensitive material this nation has" because "it protects all the other critical secrets," a former top-ranking official of the National Security Agency testified today.

"Give me access to your codes, give me access to your ciphers, and I don't need any of your other secrets," said Earl D. Clark Jr., who retired last month as NSA deputy chief of communications security. "You cannot put a price on cryptography."

Whitworth, 46, the last of the four men charged in the Walker spy ring to stand trial, is accused of passing the Soviets copies of the daily-changing codes, called keycards or keylists, along with design manuals that would allow them to build the coding machines. Armed with both components, experts say, the Soviets would have been able to decipher scrambled Navy satellite broadcasts.

In the first full day of testimony, Clark demonstrated for the jury of seven women and five men the use of what he termed "the real, live crypto equipment" -- a KW-7, a gray metal box the size of a small microwave oven and adorned with various knobs and dials. "As you can see, we don't make them very sexy, but they do perform a very sexy function," Clark said.

The Whitworth trial is believed to be the first time a coding machine has been brought into court, NSA officials said, and the first time the KW-7, which Clark said is still in use, has been shown publicly. Clark said outside the courtroom that the NSA decided to permit the showing of the KW-7 after "some debate."

Standing before the jury, he lifted two circuit boards out of the device. "They are the guts," he said. "If a hostile intelligence organization is able to obtain the information contained on these boards, that organization in all probability is going to be able to construct a device that can read our most sensitive communications."

Clark inserted a computer key card into the machine, and each juror was given a packet of the cards produced by the NSA for the Whitworth prosecution.

"Crypto key is the most highly prized possession of one country against another," Clark testified. "There is no question in my mind that it is one of the top targets of the Soviet intelligence organization."

Neither Clark nor an earlier witness today, Rear Adm. Lawrence Layman, the director of naval communications, mentioned Whitworth by name. Their testimony, however, was aimed at showing the importance of the material Whitworth allegedly passed to the Soviets and the length to which the government has gone to try to protect the security of the communications that Whitworth allegedly compromised.

One of the biggest loopholes in the system, Clark said pointedly, is "when a cleared individual who has access to cryptographic key for some reason decides to work for a hostile intelligence organization . . . . The system to a large extent is based on trust in the person."

"Because we entrust our radiomen the highest classified information the Navy operates with, we must have confidence that they have . . . character and integrity," Layman said.

The jurors also were instructed in the intricacies of the jargon-studded, acronym-laden world of military communications.

Layman's testimony touched on such topics as procedures in the "crypto room" aboard ships where "secure" messages are "decrypted," the relative advantages of ultrahigh-frequency satellite relays and high-frequency shortwave transmissions, and the function of the NAVCOMPARS -- the Naval Communications Processing and Routing System -- in routing messages.

At different times, both Whitworth and admitted spy John Anthony Walker Jr. controlled the cryptography vault aboard the USS Niagara Falls. Whitworth is charged with passing documents through Walker to the Soviets from 1974 until Walker's arrest last May 20. Whitworth allegedly received $332,000 for this role in the conspiracy.

Prosecutors William S. Farmer and Leida Schoggen want to educate the jurors about the importance of naval communications and the role that Whitworth played as a communications expert during his 23 years of service.

Layman made a direct reference to the current confrontation between the United States and Libya when he told the jury that all messages, whether classified or not, are coded so that "the enemy" will not know whether they are routine communications or "a top secret flash message reporting an enemy sighting in the Gulf of Sidra."