Mary Hartman has run off with Sgt. Foley. Tom Hartman lives in his car. Merle Jeeter is so broke he's auctioning off toothbrushes on Main Street. Loretta Haggers went on the road and wakes up one morning in bed with a roadie, while her husband Charlie, at home, finds himself in conspicous conjugation with a certain Sophia.

And George Shunway, who seemed a goner when he fell into a vat of Rust-O-Leum, has been throught four months of plastic surgery and turned into a crotchety dreamboat who looks very much like Tab Hunter.

Nothing much has changed in Fernwood.

"Forever Fernwood," premiering tonight at 11 o'clock on Channel 20, proves that "Mary Hartman, Mary Hartman" can survive without mary Hartman - that is, Louise Lasser, who really had done about as much with her role in this biodegradable comic soap opera as could be done. But neither the show's fiver writers, two story consultants, program consultant, creative supervisor, two producers, two story and script supervisors, nor any of the other contributors has come up with a substitute centrifugal figure.

There remains about the show, though, an abiding sense of aghast bemusement that mellows the grotesquerie and makes it sometimes profound. "Forever Fernwood" is a nightly testimonial to the infinitely varied says people can foul up their lives. In this pursuit it has a bottimless reservoir of potential materila.

many of the old characters and actors are back joined by such newly-discovered wrecks as Eleanor Major (Shelley Fabares), a tennis player crippled in an accident immediately after winning the Wimbledon, and the pathetic, stammering sister (Judy Kahan) she keeps captive.

Also, there is Tab Hunter.

A tackily resplendent new Main Street set, its kwikee Mart and Bijou Theater glistering in studio sun, is explored profitably by director Jim Drake's cameras on the premiere, which also includes a visit from Rona Barrett as herself. Miss Rona, stranded in Fernwood by accident - which is the only way to get there, really - helps with the exposition by interviewing the bartender at the Capri Lounge.

Perhaps because we can now compare it to the crude, crueler "Soap," Norman Lear's "Fernwood" seems increasingly warm and relevant, its back-door appraoch to reality a comfy antidote to the mentality that dominates prime time. Fernwood has become the "Our Town" of the '70s.

Meanwhile, "Fernwood 2Night," the mock talk shoe that ended last week, has a future after all. A Lear spokesman says production will be resumed near the end of the year for telecast in early 1978. It couldn't happen to a nicer malicious travesty. 'VTR'

Television is not an art from but video can be. The difference will be demonstrated on "VTR - Video and Television Review," which premiers on Channel 26 and other public TV stations at 10:30 tonight.

The first program in the six-show series samples the work of pioneering video maverick William Wegman, who makes most of his short, personal, black-and-white tapes in his own room with the door locked. The only other participating artistic voice is that on Man Ray, Wegman's achingly cooperative dog. One tape consists of Man Ray watching marbles roll by on a table and finally catching one of them in his mouth. It's superb.

For Wegman, the video screen is an electron canvas on which to play games of prank art. His camera rarely moves as subjects move in and out of the frame. The work, dating back several years, is refreshingly direct and uncluttered as communication.

Public television should present more such individualistic, innovative video and waste less time on tired art forms from other centuries. In fact, commercial TV beat public TV to this punch several weeks ago - some of Wegman's arresting little brainstorms were aired on "The Tonight Show Starring Johnny Carson."