The possible seizure, intact, of United States coding equipment by Soviet agents or others in the occupied US Embassy in Iran would be only one of a series of serious breaches of US communications security since the 1960s.
Hostile assaults or penetration of this security included:
* The 1967 Israeli attack on the US intelligence ship Liberty off the Sinai coast.
* Seizure of the Pueblo, a similar but smaller vessel, by the North Koreans in 1968.
* The 1974-75 transfer by two Americans to Soviet agents to plans for two "spy-in-the- sky" satellites, complete with computer chipher key cards and clear-text messages (enabling Soviet cryptanalysts to solve the chiphers used), plus a supersecret plan, code- named Pyramider, for a worldwide, miniature, instant Central Intelligence Agency communications system -- also by satellite.
* The 1978 sale to the soviets in Athens of a top-secret manual on another major US satellite system. Former CIA employee William Kampiles was sentenced to federal prison in the case.
* Iranian takeover of top-secret US monitoring stations on the Soviet frontier during the overthrow of the Shah a year ago.
The 1974-75 case, in which Californians Christopher John Boyce and Andrew Dalton Lee Exchanged the plans to TRW Corporation's Rhyolite and Argus satellites to Soviet agents in Mexico City, is described in a new book, "The Falcon and the Snowman," by John Lindsey, just published by Simon & Schuster.
Exas Gov. William Clements Jr., who was deputy secretary of defense while Boyce and Lee were selling the material to the Russians, commented on the TRW case: "Our intelligence community is in disarray. A major satellite intelligence system, developed and de ployed at a cost of billions of dollars over the past decade, without Soviet knowledge, has been compromised by intelligence procedures as porous as Swiss cheese."
Boyce and Lee were sentenced to 40 years and life imprisonment, respectively, for espionage. Shortly after the TRW and Kampiles cases, whether by coincidence or not, the Russians began encoding the telemetry -- electronic emissions -- from their rocket and missile tests. This made US interpretation of them far more difficult. It made doubly important the monitoring sites which the US lost in Iran, but which it still operates in Turkey and elsewhere.
This led to serious doubts inside the intelligence and arms-control communities about American ability to verify the now-delayed SALT II arms-limitation treaty with the USSR.
When militants seized the US Embassy in Tehran, some files and equipment were at least partially burned, as prescribed, during the two to three hours between first warning of the assault and final occupation of the entire embassy compound.
Top US officials have been unable or unwilling to comment on reports that "outside experts" of unknown nationality were allowed by the "students" holding the embassy to examine, then remove, communications equipment, including cipher machines, to which thermite bombs normally are attached for their destruction. This reportedly was accomplished in the code room of the American Embassy in Islamabad, Pakistan, when mobs attacked it last November.
There is some reason to believe that eqiupment might have been lost, not during the current occupation of the Tehran embassy but during the Feb. 14, 1979 , temporary takeover when Ambassador William Sullivan was briefly held hostage.
LEading cyrptographic expert David Kahn, who wrote "The Code Breakers," a comprehensive history of secret communications, said in a telephone interview that, although he had no inside knowledge of what might have been lost at the Tehran embassy, "our newest systems are very, very strong, and the loss might not have been too serious.
"Of course," Mr. Kahn added, "they could get a good overview of our entire systems if they got whole machines intact, together with printed circuit boards and keying cards. If they got only the machines, or a part of the whole system, it would be doubtful that they could read our traffic."
High-grade, modern crypto-systems employ computers that use an infinitely varying key, which can be solved either not at all or only by exhaustive use of another, similar computer, Mr. Kahn explained.
Cryptanalysis of German and Japanese ciphers and codes considerably speeded allied victory in world War II, in the opinion of leading British and US intelligence experts who have described their victory in a number of books.
Supervision of US cryptology, including security and US efforts to solve systems of other countries, is the responsibility of the supersecret National Security Agency under Defense Secretary Harold Brown and directed by Vice-Adm. Bobby R. Inman, with headquarters at Ft. Meade, Md.