"The Amityville Horror" is a feeble excuse for a haunted-house thriller, but given the source, who could ask for more?

"The woefully pedestrian best-seller, fabricated at the urging of an editor at Prentice-Hall and promoted as a "true" account, may have become the most profitable dog-ate-my-home-work story every told.

Book and movie purport to chronicle the strange, terrifying sequence of events that drove young George and Kathleen Lutz and their three kids from a newly purchased home in Amityville, L.I., after a mere 28 days in residence.

The alleged haunted house, a three-story, six-bedroom Dutch colonial, dominated an expansive waterfront lot. (The house in the movie version, shot on location in Toms River, N.J., offers a guest cottage in place of the original swimming pool - but neither figures in the mystery anyway.) The property was available for a bargain $80,000 because the previous owners, the DeFeos, had met a tragic fate: They were shot to death one night by their son Ronald, who also murdered his two brothers and sisters.

Lutz, who operated a land surveying company, jumped at the bargain. The family moved in on Dec. 18, 1975 and supposedly ran for their lives on Jan. 15, 1976, after suffering frights, injuries and personality changes too appalling to be tolerated a day longer. Following publication of the book and assorted spin-offs (including a byline rehash by Kathleen for The National Enquirer, the Lutzes relocated in San Diego and Said No More. The house in Amityville was soon purchased by another family which has lived there without supernatural incident.

The only authority for the supernatural horror story is the Lutzes themselves, and the account in the book usually sounds desperately farfetched, padded and anticlimactic.

The Lutzes barely function as suspense story characters, let alone authentic human beings in danger. By turns absurd and oblivious, their reactions to the malign forces supposedly making the house unlivable recall the ghost-chasing antics of Abbott & Costello, The Bowery Boys and The Three Stooges.

The film version, listlessly faithful to the book, does almost nothing to improve or reinforce its scare tactics. The opening shot of the house is witty: two quadrant-shaped windows on the third floor look like demonic red eyes, and the entire facade is framed and lit in a way that suggests a giant jack-o-lantern. It's all downhill from there: The movie doesn't get any wittier, the house doesn't get any creepier, and the filmmakers don't seem to be trying too hard.

During the first 90 minutes the scariest sight is a black cat who suddenly appears outside a living room window. No, the second scariest. It's far more frightening watching Rod Steiger act. He plays Father Delaney, a priest who is tormented into insanity for simply trying to bless the house, an act that evidently offends the resident deamons profoundly.

Poor Steiger now looks like W. C. Fields, but his acting is not meant to be as hysterically funny as it is. He just can't restrain himself when permitted to blubber, shriek a line like "I am a trained psychotherapist!" and go to bonkers while conducting a mass.

Although Margot Kidder proved herself a pheonmenal screamer in "Superman," she gets only one opportunity to rattle the rafters in "The Amityville Horror" - upon awakening from a nightmare. It couldn't have been easy characterizing a phantom heroine like Kathleen Lutz, and Kidder doesn't get much further than wearing her hair in pigtails to look at once cute and practical around the haunted house.

As George Lutz, James Brolin is supposed to be the big threat, since living in the house turns him into a potential murderer. He's closer to a big prop, and the movie is virtually over before director Stuart Rosenberg succeeds in maneuvering him into threatening positions, which everyone understands to be a fakeout anyway. Adorned with a vaguely Christlike beard and unruly mane, Brolin is rather too laid-back to capitalize on the resem0lance. Neither mad nor divine, he's just drowsy. That's in the spirit of the movie itself, a horror thriller ideal for a two-hour snooze.

Being presold, the film version of "The Amityville Horror" should do a good business until the news about its lack of thrills gets around. The titles, which announce "The First Day...the 7th Day...the 12th Day..." etc., have an uncanny way of underlining the plodding continuity. With each new title you think, "How alike these days are and how devoid of incident!" What a relief it is to see "The Last Day..." CAPTION: Picture, Margot Kidder in "The Amityville Horror."