For those accustomed to watching him, Marvin Mandel's first post-conviction television appearance last week held no surprises.

For a full hour, Mandel looked his audience straight in the eye, tightened his lips in his most sincere, dramatic way, and evaded, fudged or deflected every important question he was asked.

When he was governor, such performances were routine but exasperating. Last week's performance was simply sad, even pathetic.

There was the classic Mandel non-response when asked if his friends were supporting him financially to help him pay the $675 a month rent at his five-acre estate in Anne Arundel County.

"I haven't asked any friend for any help," he said, not saying if he were getting any unsolicited support.

There was the standard Mandel contradiction when he said he was dippling into his own and his wife's savings to pay his way. At his trial, he testified that he and his wife had exhausted their funds and therefore had to take money from the Pallotine Fathers religious order to make ends meet.

There are the carefully phrased non-answers to questions never asked. Did anyone ever testify, he wanted to know, "that I asked them to do anything improper?" as if such testimony were even relevant to his recent conviction on mail fraud and racketerring charges.

Some of it was almost comical. His true enjoyment, said a governor who surrounded himself with a phalanx of burly state troopers, was mingling with "the people." He had made his "own way," in life and had never been handed anything, said the governor who received thousands of dollars in gifts, (down to the clothes on his back) from rich friends.

"No one made it for me," he said. He was so glad now to finally have a chance to relax and be with his family, said the man who spent a good part of his second term vacationing in Jamaica, Florida, Europe and Ocean City.

As governor, there were those who said Mandel was incapable of giving a straightforward and candid statement about anything. Even some of his closest friends and advisers were stunned by the frequent gratuitous, useless and inexplicable untruths for which he became famous.

In 1975, for example, Mandel presided at a press conference called to unveil a voluminous report on education in the state. When asked his opinions on the report, he said repeatedly he had not read it.

The chairman of the commission. Leo Rosenberg, shook his head incredulously as he walked to his car with a reporter after the press conference.

"I don't understand it," he said. "The governor read that report and we discussed it at great length. And then he goes out there and says he hasn't read it. I don't understand it."

On another occasion, Mandel met with Baltimore Mayor William Donald Schaefer and Baltimore police commissioner Donald D. Pomerleau to discuss the theft of heroin from the police department's evidence room. After the meeting, each man was asked if the theft had been, as expected, the topic of conversation.

"Of course we discussed the heroin," said Schaefer. "We did discuss the theft of heroin" said Pomerleau. "No, the subject didn't even come up," said Mandel.

On a third, more serious occasion, Mandel insisted that he never took any trips at the expense of businessmen, beyond the famous trip to Jamaica in 1974. Within the next week, his spokesman, Frank A. DeFilippo, acknowledged that Mandel had taken at least 10 other all-expense paid trips.

The former governor's television appearance was, if nothing else, instructive to those who wondered how he could have ever gotten into so much trouble.

The case against Mandel boiled down to one of fraud - deception and lying. If Mandel committed each of the acts which the prosecutors alleged, but had leveled with the public about it at his press conferences between 1972 and 1975, he would undoubtedly still be in office.

Mandel, like so many other disgraced public officials, now hopes to market a book about his experiences. No one expects a confession. But some of his associates worry openly that such an undertaking could never get off the ground if the governor refuses to at least create the appearance that he is being candid.