"Murder by Decree,c a stylish new Sherlock Holmes mystery, is graced by the amiable teamwork of Christopher Plummer and James Mason in the roles of Holmes and Watson, respectively. Like Nicol Williamson and Robert Duvall in "The Seven-Per-Cent Solution," they contradict the tradition of the Basil Rathbone-Nigel Bruce series, closing the gap between intellects and suggesting a much more equitable friendship. Mason's grave, thoughtful, stalwart Watson is especially satisfying: a phlegmatic type, but nobody's fool.

Screenwriter John Hopkins interjects Holmes and Watson into the Jack the Ripper case. While never as playful or ingenious as Nicholas Meyer's screenplay for "The Seven-Per-Cent Solution," Hopkins' mystery is crisp and chilling right up to the demouement.At that point it might be wise to edge toward the exits, since the solution leaves much to be desired.

Perhaps carried away by the socalled Watergate Morality, Hopkins porttrays the Ripper murders as a conspiracy indirectly implicating Prominent Persons. When the conspirators are unmasked, it comes as a letdown to realize that they were peripheral figures. Hopkins never gets the suspects centrally located in the plot, a failing that also makes it difficult to follow their bloody path to the door of the Establishment as fervently as one is urged to do.

Hopkins tries to tie up the loose ends by giving Holmes an outrageously sanctimonious and idealogical speech in which he takes to task the prime minister, portrayed by John Gielgud, for permitting gruesome things to happen to society's outcasts. Even if Holmes uncovered a case that might prove embarrassing to the ruling class, it's difficult to accept Hopkins' sentimental notion that he might scold or threaten the authorities. If anything, his class interest probably would dictate sparing the crown embarrassment as much as possible. The scandal itself is dubious, and Holmes seems the wrong type to express indignation about it.

The director, Bob Clark, has begun to show a dry, explosive flair for menacing situations. His las feature, "Breaking Point," has worthless script but sustained some vivid interludes of lurking terror. "Murder by Decree" allows him to lurk even more effectively in the gloom of fogshrouded London's streets, alleys and nooks.

Clark, an American, knows how to get you by the throat after building up a suffocating sense of apprehension. One might even complain that he goes for the throat a little ruthlessly. The Ripper atrocities are documented with explicit, clinical ghoulishness. From time to time Clark's orchestrations of terror also partake of too much virtuosity for their own good. Reconstructing the first murder, for example, Clark resorts to a subjective prowl through back streets that recalls so closely the first shark attack in "Jaws" that the effect is slightly comic, scary atmosphere or no scary atmosphere.

The freshly attractive aspect of Clark's direction is his astute concentration on the actors. The good performances merely begin with Plummer and Mason. There's an impressive gallery of supporting players: Donald Sutherland as a pale-eyed, soft-spoken clairvoyant; Genevieve Bujold in a scintillating cameo as a cruelly deceived patient at a secluded Bedlam; Susan Clark as a frightened prostitute; David Hemmings and Frank Finlay as worthy representatives of Scotland Yard.

Like "Agatha," "Murder by Decree" is deft and amusing enough to survive the disappointing sags in its fabric of mystification. Holmes and Watson have pursued more interesting and plausible cases, but it's enjoyable to watch the case being pursued by the exceptionally human, vulnerable gentleman detectives embodied by Plummer and Mason