"Beware of the dwarf," whispers a dying man to an oblivious Goldie Hawn in the early going of "Foul Play." Cast as a nitwit librarian who becomes innocently entangled in a murder conspiracy, Hawn is supposed to act dumb.

There's no such excuse for the screenwriter. Colin Higgins, who makes an inauspicious debut as his own director after rising to prominence with "Harold and Maude" and "The Silver Streak."

Eager to fabricate escapist entertainment. Higgins can't keep his mind from wandering. "Foul Play" never begins to make sense as a mystery 3 Dudley Moore and the 3-foot-9 Billy Barty, become the butts of grotesquely conceived and staged sight gags.

Higgins comes close to stranding Chevy Chase in his debut as a romantic lead. Chase appears in a pre-credit teaser making a bumbling, lewd attempt to pick up the heroine at a party. Over half an hour goes by before Higgins remembers to get Chase back on the screen. By that time his notion of darling ingenuousness, but she fares better than Chase. Her role is fundamentally mindless, and therefore insulting, but when her giggly, wide-eyed vivacity flickers into view, one feels grateful for small favors.

"Foul Play" is essentially a reprise of "The Silver Streak": a fouled-up, kinked-up attempt at a playful romantic comedy-mystery in the Hitchcock tradition.

It's obvious what Higgins wants to do: make romantic comedy thrillers as polished and satisfying as "The 39 Steps," "The Lady Vanishes." "Rear Window," "North by Northwest." "Charade" and "The Prize." It would be a blessing if he could.

There happens tobe one in town, but it isn't "Foul Play." Philippe De Broca's "Dear Inspector" actually blends the sort of ingredients Higgins keeps straining to whip into frothy shape.

In his efforts to emulate Hitchcock and the better initators of Hitchcock. Higgins resorts to techniques that resemble nothing so much as the misguided come-ons he ridicules in the Dudley Moore character. As a movie stylist. Higgins too is inexpert. Perhaps his deficiencies as a storyteller account for the grotesque mixture of sentimentality and sick humor that gums up his work.

"Harold and Maude" combined inspirational platitudes with running gags about facetious attempts at suicide. The harmless fun in "The Silver Streak" was punctuated by excessive, bloody outbursts of violence. "Foul Play" never establishes a secure lone and rhythm. It fluctuates between heavyhanded attempts at light comedy and shocking scare sequences. The true significance of the drawf clue is that it betrays a primitive fear mechanism in Higgins himself. He perceives little guys as stooges and deploys a tall albino and a scarface as menaces in ways that recall apprehensions about coming into contact with "freakish" individuals.

When Goldie Hawn is threatened by ominous settings or beastly characters, one readily identifies the thriller atmosphere being recalled. In a similar respect one recognizes the romantic comedy impulse behind the sexual sparrings of Hawn and Chase. It's the execution that leaves everything to be desired.