The Strategic Air Command's chief legal adviser yesterday insisted that he had assented to an honorable discharge for 2nd Lt. Christopher M. Cooke only if Cooke turned out to be "a naive schoolboy" and not a Soviet spy.

Taking the stand after a week of defense efforts to depict him as a liar, Brig. Gen. C. Claude Teagarden also protested that he never approved any offer of immunity to Cooke, who faces 52 years at hard labor on charges of espionage and related offenses.

Instead, Teagarden said he laid down conditions for Cooke's release last May 9 that hinged explicitly on an account Cooke had given to Air Force investigators already.

Teagarden said a top official of the Air Force Office of Special Investigations (OSI) had led him to believe that a statement Cooke gave OSI investigators on May 7 was truthful and that Cooke's unauthorized contacts with the Soviet Embassy were those of "the naive schoolboy simply pursuing interests he had pursued as a college student."

The testimony conflicted directly on numerous points with the courtroom accounts of Air Force officers called to the stand by the defense. Cooke's first military lawyer, Capt. Francis W. Pedrotty III, testified Friday that he repeatedly extracted oral promises of "no prosecution" from Teagarden on May 9 if Cooke would simply start telling the truth.

Pedrotty said he had tried to extract a written grant of immunity, but dropped the effort after the general warned him of "the wrath of Teagarden" if he persisted.

Belying his reputation with a genial smile, the bald, 46-year-old Teagarden said he first heard of Cooke, who was then deputy commander of a Titan II missile crew in Kansas, last April 27.

Teagarden, staff judge advocate at SAC headquarters in Omaha, said an OSI colonel there told him there was "reason to believe that Cooke had been inside the Soviet Embassy" here last Dec. 23. Close surveillance was ordered for a leave Cooke was to take.

Teagarden said he was informed by OSI officials on May 5 that Cooke had flown to Washington National Airport three days earlier and had taken a taxi to the Soviet Embassy. Teagarden said he ordered that Cooke "be picked up immediately off the street, advised of his rights . . . and questioned."

This conflicted with the testimony of Air Force Maj. William T. Snyder, then OSI's legal counsel, who said Teagarden's instructions were "to advise him of his rights, but if he asks for a lawyer, press on."

Snyder said the OSI decided that Teagarden could not "have it both ways," and eventually got Teagarden's approval to question Cooke without advising him of his rights. OSI officials said they thought this meant that SAC was more interested in finding out what secrets Cooke had compromised than in prosecuting.

Teagarden, however, indicated that he and Gen. Richard Ellis, then SAC's commander in chief, soon became disenchanted with OSI's handling of the case.

Teagarden said that on the evening of May 8 he was told that Cooke did not want to take a polygraph examination to verify the 17-page statement he had given the day before, a statement that Cooke's lawyers have described as full of "lies."

The next day, May 9, Teagarden said, he was called by Capt. Pedrotty, who had just been assigned to defend Cooke.

"He said, 'General, in order for my client to take the polygraph, SAC is going to have to give . . . some assurances,' " Teagarden testified.

Teagarden said he had been considering an honorable discharge as an inducement for Cooke to take a polygraph test. He said he explicitly told Pedrotty that Cooke could have one "if the May 7 statement is true and wholly true, if he takes a polygraph, and if the polygraph shows his statement to be true and wholly true."

Teagarden said Pedrotty called him back later and informed him that "my client wants this in writing." Teagarden said he refused.

"I said, Frank . . . the ball is in your court . . . . I said there's only two people that know the truth --he Cooke and Ivan ain't talking . . . . It was just as simple as that . . . . It ain't going to be in writing."

Teagarden also said there was "absolutely no" discussion of immunity. "If there had been," he said, "it would have been very simple. I have no authority to grant immunity."

Pedrotty has denounced the account, which Teagarden first gave during pretrial proceedings, as "completely ludicrous." It has also been disputed in all important particulars by Cooke's chief Air Force interrogator, OSI Lt. Col. Jerome Hoffman, who said he heard the discussions on an extension.

Teagarden said he thought he had two conversations with Pedrotty, and said he did not remember Hoffman's being on the line. "I'm not going to fall on my sword about that," he added.