The man in the plaid flannel spacesuit talks about his series

Some people have to see Simon Jones in his bathrobe in order to recognize him.

He is earthling Arthur Dent in the new cult series Hitch Hiker's Guide to the Galaxy (PBS, check local listings for day and time, or call local program manager if not listed, since station may not schedule it unless it is requested). Dent has been kidnapped in his dressing gown and taken for a trek round the galaxy. Thus, throughout the entire seven-part series now airing throughout America, Mr. Jones's wardrobe consists of an ugly plaid flannel bathrobe.

Jones arrived to be interviewed sans bathrobe. But he said he had brought it with him on this promotional tour of America. ''Without it,'' he reflected just a bit sadly, ''nobody recognizes me.''

Then he smiled when he remembered the time he visited a bookshop in Mill Valley, San Francisco, and a man reading the Sunday newspaper looked up and said 'I like your work,' then returned to his reading. ''The cheek of it,'' says Simon, ''you'd think Mill Valley was the center of the universe and, of course, I should be there. Extraordinary.''

Mr. Jones is a graduate of Cambridge and the Footlights Revue Club like most of the Monty Python crew, as well as Jonathan Miller, David Frost, and Douglas Adams, author of the ''Hitch Hiker'' series. Simon speaks with a very upper-class ''public'' school accent. Very much like the accent he used when he played Sebastian's stuffy older brother, Bridey, in ''Brideshead Revisited.'' But he asserts that the closest he ever got to the nobility was when his father served as the agent for a nobleman's estate in Wiltshire.

Why is it that esoteric, slightly elitist ''Monty Python'' humor arises out of Britain's universities, while the US tends to get coarse ''Animal House'' humor out of our universities?

''Some of the British elitist humor stems from the fact that BBC has been monolithic for 60 years, looking toward its own people, making certain they get air time. But don't forget that Benny Hill (a more blue-collar-style British comedy series) is very much more popular than Monty Python in England.''

Was ''Hitch Hiker'' a cult show in England, revered as it is here by a small band of enthusiasts?

He laughs. ''Yes. Some of my friends have not understood a word of 'Hitch Hiker,' believing it to be much more clever than it is. All it does is take a swipe at all kinds of bureaucracy by inflating it to intergalactic proportions and thus making it look silly.''

But doesn't it also poke fun at science fiction pomposity?

''Oh, yes, it certainly gives a nod in that direction, but the science fiction fans don't feel they are being mocked, it is such an affectionate mocking. They are fanatically supportive of it. After all, we are using their conventions.''

How does it feel to be a culture hero?

''How much of a culture hero am I, when I have to wear a dressing gown to be recognized? I've gotten a few letters - you could count the number on the fingers of one hand. I just heard that there has been an Arthur Dent Appreciation Society at London University for several years. Nobody ever bothered to tell me.''

Jones believes that ''Hitch Hiker'' pinpoints the generation gap. ''Older people switch it off and think it silly; young children seem to understand every word of it. As a matter of fact, the series should encourage the sale of videotapes and recorders, since almost nobody can take it all in the first time around. The graphics and the plot go by so fast, they must be seen again.''

Besides being in American cable reruns of ''Brideshead Revisited,'' Jones will also soon be in several new films - ''Giro City'' with Glenda Jackson, ''Privates On Parade'' with John Cleese, and in a bit part in the new Monty Python movie, ''The Meaning of Life.'' He admits to having played an unbilled minor part in the recent Warren Beatty epic, ''Reds.''

Will there be more of the ''Hitch Hiker'' series?

He shakes his head, resignedly. ''Although it was a successful BBC radio show before it became a successful BBC-TV show, I don't think BBC is prepared to finance it again, even though costs were puny by American standards. They didn't think enough of it to publish the book, which has now sold millions (put out by another publisher), or to issue the record, which is only available as an export from England.''

Did BBC pay for the original bathrobe?

He puts his finger to his lips. ''Shush, . . . it still belongs to them, although I have it with me in America for appearances on talk shows. . . .''

Doesn't Simon agree that the robe really ought to be donated to the Smithsonian Institution to be displayed beside Archie Bunker's chair and Mary Tyler Moore's typewriter?

''Perhaps,'' he says, his eyes filled with Arthur Dent-like glee. ''But then, what would I wear when I want to be recognized?''