Television pictures from China still seem nearly as exotic as television pictures from Jupiter; so much of it remains unseen. A huge void now begins to be filled, most notably with the current 12-part British documentary series "The Heart of the Dragon," whose third installment, "Living," tonight at 8 on Channel 26, examines life in the small, agrarian mountain village of Maoping in southeast China.

Life in the village has remained largely unchanged for centuries, revolution or no. People harvest bamboo and rice, make baskets, carry charcoal down slopes, and cook. The most exciting thing in Maoping in recent years appears to have been the arrival of four color television sets. At night a large portion of the village populace gathers in a hall to watch a travelogue.

One wonders what they would make of "Lifestyles of the Rich and Famous."

Long white noodles dry in the afternoon sun, a single shaky truck seems to constitute all the traffic on the village streets, and the overall impression given of village life is of uninterrupted tranquility.

On the surface, this may appear to be a dull hour chronicling the routine and the mundane. Many of the scenes and conversations, in addition, look staged and static, too tidy to be true. And yet there is a real seductiveness to this vision of 20th-century life untouched by the jet engine or the computer, and to a landscape devoid of satellite dishes or golden arches.

The narration, spoken by Anthony Quayle, is nonjudgmental. Given the current rabidly anticommunist political ambiance (the only thing as humorless as communism is anticommunism), "Dragon" might be criticized in some quarters for its lack of the occasional smug nudge about the bleakness of regimented life in a totalitarian state. The producers prefer to show it rather than tell it, however. And so there is a slight but perceptible chill to a sequence shot in a schoolroom where a teacher speaks to tiny tots of "the spirit of the proletarian revolutionaries" and a little boy rises rhetorically to declare, "When I grow up, I'm going to be a hard-working and brave peasant."

Just as in this country, the farmer is threatened with extinction, though in China it's not so imminent a worry. This episode of "The Heart of the Dragon," though, is memorable not for social or political observations, but for the sublime and intoxicating peacefulness of the valley in which it all takes place. The program is nearly as unhurried as life appears to be in Maoping; it is doubly evocative.

Peter Mackay did the photography, Mischa Scorer wrote and directed the program, and Peter Montagnon was executive producer. Because either Jim Lehrer or Robert MacNeil (tonight, Lehrer) appears at the open and close of each episode, and because General Electric gave a grant to them for importing it, this becomes a "MacNeil-Lehrer-Gannett Production." Instead of a simple identifying legend or trademark, GE's funding credit is a handsomely produced mini-commercial obviously made by a high-priced ad agency. Thus does the pollution of "public" television continue, though for the chance to visit China, one is willing to suffer it. 'Forty Years Together'

Inadvertently, no doubt, WTTG-TV reveals one hallmark of its programming and operations during the anniversary special "Forty Years Together," at 8:30 tonight on Channel 5; it has always been a pretty cheap outfit, and also, at least in the past decade or two, an extravagantly profitable one. The half-hour look back is little more than a program-length promo for the station, not the nostalgic voyage a viewer might reasonably expect.

There are glimpses of Channel 5 local shows from the past: "Pick Temple's Giant Ranch," "Dugout Chatter" with Bob Wolff (the George Michael of his day?), and "Captain Tugg," who piloted the Channel Queen down make-believe waterways. The producers also unearthed clips from programs produced by the Dumont Network, of which Channel 5 was a member during the network's relatively brief existence. We see Jackie Gleason on "Cavalcade of Stars," Art Carney as a guest on the Morey Amsterdam show, Ernie Kovacs reciting a French version of "Snow White" and so on. The clips are either oddly chosen or oddly edited or both.

Current WTTG on-air personalities (to stretch a term, in some cases) host the show in footage taped on the run at a recent black-tie party to herald the anniversary. Perhaps if the management had spent less on the party and more on the special, viewers might have been tricked into thinking there really was something to celebrate.