Zorro, the Spanish word for fox, is the alias chosen by Don Diego Vega, a crafty young nobleman of Old California, to conceal his exploits as a crusading masked outlaw. An exotic western synthesis of the Scarlet Pimpernel and Robin Hood, the character was introduced by Johnston McCulley in a story called "The Curse of ycapistrano." Zorro became a durable movie facorite in 1920, when Douglas Fairbanks starred in "The Mark of Zorro."

Now George Hamilton, seeking a follow-up vehicle to "Love at First Bite," has seized on Zorro as a likely subject for amiable parody. Not a bad idea, but it may have been an idea destined to read funnier than it plays. The finished film, "Zorro, the Gay Blade," opening today at area theaters, is a haphazard example of giddy entertainment.

Zorro is well within Hamilton's late-blooming comic range, and his approach to the role is obviously conceived with Fairbanks in mind. When Hamilton underlines Zorr's heroic zest by flashing an exaggerated toothy smile, he's paying homage to a gleaming leer originated by Fairbanks. In addition, the most savory comic conceit in Hal Dresner's screenplay is in confusing the opposition with two Zorros. The idea of sibling masqueraders with radically different personalities and sexual predilections is derived from a playful familiarity with the original charactr, who affected foppish manners by day in order to deflect suspicion.

Hamilton's Zorros, the flamboyant but straight Diego and the gaudily gay Ramon, are supposed to be long-separated sons of the founding Zorro, whose heroic example beckons from the grave. To be exact, Diego goes into action after he discovers Dad's old costume and reads a letter urging him to revive the tradition: "This sword, with which to fight injustice; this mask, with which to deceive tyranny; and this hat, which needs reblocking . . ."

An injury curtails Diego's double-barreled crusade against the local tyrant, Esteban, played by Ron Leibman. While aiding the oppressed populace in the guise of Zorro, Diego has been consorting with Leibman's wife, Brenda Vaccarro. Ramon arrives unexpectedly and agrees to play Zorro while Diego is convalescing. The disguise is altered in certain ways: Ramon exchanges Diego's basic black outfit for plum and other yummy colors, and his weapon of choice is a bullwhip rather than a saber. Diego frets about the disparities, but Ramon's showier style actually seems to enhance the deception.

The years away from home evidently made a new man of Ramon. He acquired another identity -- Bunnyu Wigglesworth, an officer in the British Navy -- and though he returns to the hacienda a fop, he's an accomplished fop. His imposture also produces curious effects on the villain and the heroine, Lauren 'utton as a revolutionary Yankee agitator named Charlotte. No longer suspecting Diego of being Zorro, Esteban begins to betray signs of a solicitude not unlike his wife's. Charlotte's infatuation with Diego's Zorro is intensified when she mistakes him for Ramonhs Zorro. Imagining that she's seeing a whole new "sensitive" side to the man she already adores, Charlotte displays an ardor that baffles Ramon.

This case of mistaken identity may be the most original element of character humor Dresner dredges up while rummaging around for anachronistic laughs. Dresner also has a flair for wacky wordplay particularly appealing to juveniles; for example, the noblemen who introduce themselves in the following style: "Don Jose from San Fernando . . . Don Fernando from San Francisco . . . Luis Obispo from Bakersfield." In a similar respect, Diego's Zorro hits a characteristic rhetorical snag when he vows to "help the helpless, befriend the friendless and defeat . . . the feetless."

Despite this sporadic funny stuff and the enthusiastic cast members, "Zorro" degenerates into a ponderous trifle. By turns, Peter Medak's direction seems stuffy and scattered and Hamilton's Spanish and English accents keep getting lost on the soundtrack.

"Zorro" shouldn't encounter much audience resistance, particularly if it ends up being patronized by kids. It's a harmless comic wheeze and the tedious stretches may be easy to slough off in an idle, undemanding mood.