The 50-drachma ticket, apparently to some Greek sporting event, was dutifully enclosed with a letter William Kampiles sent to the Central Intelligence Agency last May 23.

Jotted down on the back of the ticket ostensibly in the handwriting of the Soviet agent who was trying to enlist him, was the address of a proposed summertime rendezvous in Athens.

"If you think there might be Agency interest," Kampiles wrote to an old CIA colleague in the accompanying letter, "I would be willing to discuss this experience in full detail."

The letter was written, a U.S. District Court jury was told here yesterday, only because CIA experts on the Soviet bloc had refused to talk to Kampiles last April - despite the fact that all they would have had to do was walk downstairs where he was waiting.

The chief expert on Soviet affairs who was contacted reportedly said talking to Kampiles might be "improper" because he was an American citizen.

Told to write a letter instead, Kampiles sent it to a collegue at the CIA who promptly put it in his briefcase and left it there - unopened - for some two months.

The testimony about the CIA bungling, which unfolded at Kampiles' espionage trial, came not from the defense but from the first witness for the government, a CIA official named George Joannides. It was his belated opening of the Kampiles letter in late July that apparently led to the young man's indictment.

Accused of selling a top-secret manual of the KH11 spy satelite to his Soviet contact, Kampiles has denied it, maintaining through his lawyer that he was simply trying to revive a frustrated dream by playing double agent in Athens on a trip there last winter.

A senior CIA official who had befriended Kampiles in his shortlived career at the agency in 1977, Joannides testified that Kampiles told him about the trip - and his dickering with the Soviets in Athens - as they sat on a bench outside CIA headquarters on April 29, 1978, the last Friday of the month.

According to Joannides, Kampiles told him of crashing a party at the Soviet Embassy in Athens one night last February and striking up an acquaintance there with a Russian named "Michael."

Kampiles, 23, who had earlier expressed a desire to work in Greece for the CIA, told Joannides that he convinced the Russian he was still with the Agency by showing him some sort of "identity documents" that Kampiles said he had once used as a CIA watch officer.

"A reference was made to Mr. Kampiles returning to Greece in late summer," Joannides recalled. He said that Kampiles also told him that "Michael" had given Kampiles an address in Athens where he could be contacted.

"Mr. Kampiles indicated he was playing the Soviets along," Joannides related. "He also stated he had received $3,000 from the Soviets."

On hearing all that, Joannides, who worked in the CIA office of legal cousel, said he told Kampiles he ought to be atlking to someone from the Soviet sector fo the Agency. He said Kampiles agreed to wait, on the bench, near a statue of Nathan Hale, while Joannides went back inside to try to find someone to whom he could give all the details.

The witness identified the Soviet-bloc expert only as a man named "Ron." But in any case, Joannides said that "Ron" not only declined to come down and talk to Kampiles. He also declined to send a colleague.

"He stated the reason was the Executive Orders [governing the CIA.] He said that it might be improper for the Agency to be contacting a 'U.S. person,'" Joannides testified.

An executive order issued by President Carter last year lays down some restrictions for the domestic "surveillance" of U.S. persons, but contains no prohibitions against such voluntary interviews. A CIA spokesman declined yesterday to comment on the Kampiles case because "it is still in litigation." But he said he was not aware of any restrictions in the executive order prohibiting CIA officials from talking to American citizens.

Joannides indicated that he argued briefly with the expert and emphasized that "Mr. Kampiles had been in touch with the Soviets in Athens . . . that he might be a 'U.S. person' but he was a former Agency employe who had come to identify "Michael" from CIA photos.

Unable to make any headway, Joannides said, he finally suggested that Kampiles might write a letter to the Agency instead and "Ron" agreed.

Joannides said he then went back outside and simply told Kampiles that "it was late Friday afternoon and I couldn't get anyone down to see him." He said Kampiles agreed to write a letter.

Back in Chicago, where he was living, Kampiles finally sent the promised letter to the Soviet Embassy recounting his visit to Joannides at his home in Potamac on May 23. He said that in subsequent meetings with Michael "we then discussed the use of a camera and his role in delivering the information." Kampiles continued, "We set the date for our next meeting during the last two weeks in August. The address Michael gave me is enclosed in the original form," he said, referring to the 50 drachma ticket.

An owlish-looking man with hornrimmed glass, Joannides, who has been recovering from a heart attack said he remembered getting the letter at his home and then sticking it in zippered briefcase that he took to the office along with doctor bills and insurance forms.

Blaming changes in assignments and status in the CIA, where he is now a part-time employe, Joannides said. "I never addressed myself to the briefcase until late July." Only the did he open the envelope with Kampiles' return address on it.

Joannides said he then turned the letter over to the CIA's Soviet section and at the request of an official there, Vivian Sacos, he called Kampiles to ask him to come to Washington to discuss the matter.

Kampiles agreed but said he was due to go th Athens on Aug. 18. He said he would try to make arrangements to come to Washington before then and promised to call Joannides back.

When he did, Joannides recalled, it was once again Friday afternoon at the CIA and "my secretary erroneously refused to put it through, saying I was in conference." Joannides said he rectified the mistake by calling Kampiles back and confirming details of his subsequent trip to Washington, including interviews with FBI and CIA officials.

Kampiles finally went back to Munster, Ind., where the FBI arrested him on Aug. 17, the day before his projected trip to Athens.