That rarity, a western - this time from Canada

There have been mighty few westerns lately, so it's no large compliment to say The Grey Fox is the best of its breed in years. But it is that - fetchingly acted, handsomely photographed, and charged with wry humor.

Richard Farnsworth plays the hero, if you can call him that. He's a mannerly gent who took to robbing stagecoaches as a teen-ager. Now it's 1901, and he's just left Alcatraz after a few decades behind bars.

Times have changed, but he hasn't. Picking up his old career, he returns to the wrong side of the law. He wants to be up to date, though. After seeing ''The Great Train Robbery'' at a nickelodeon, he switches to railroads instead of stagecoaches.

The director of this Canadian production, Phillip Borsos, puts Farnsworth at the center of almost every scene. And wisely so. With his crinkly face and soothing voice, this wily actor positively radiates a craggy charm, making his ''grey fox'' a sympathetic and even appealing old codger despite his deeds. It's hard not to like him, especially when he's wooing the heroine, a mature and independent woman who's a far cry from the mincing girlfriends of most modern films.

The picture's weak link is its psychology. We never learn why a conspicuously gentle man like the grey fox turned outlaw, or how he comes to grips with his crimes in his own mind. And we never get a good reason for staying on his side, likable though he is in many ways. Are we supposed to root for him because he has such twinkly eyes? Because he's polite? Because he only steals corporate money? He really is a bad guy, with a very large gun! And that's important not to forget, even though the movie would like you to in every other scene.

The filmmakers apparently consider the grey fox a kind of folk hero, a Pretty Boy Floyd type who somehow expresses the legitimate gripes and discontents of his time. This explains the occasional digressions into sociology, as when the characters take time to mourn a sad crime committed by a Chinese immigrant with no hope left.

But the movie works best when it settles for quiet humor and mild touches of drama - not taking much of a stand regarding the hero's skulduggery, true, but serving as a reminder that even a villain can have virtues. In its way, ''The Grey Fox'' is a human and humane little picture. And it's always nice to find another one of those.