'Romancing' charms; new 'Tarzan' beats its own chest

If you have time for only one hokey adventure yarn this season, Romancing the Stone has lots more pizazz than its pompously named cousin, Greystoke: The Legend of Tarzan, Lord of the Apes.

The trouble with this ''Tarzan'' is that it's too big, long, and self-important for the rollicking myth it wants to sell. If you've ever read a book by Edgar Rice Burroughs, the inventor of that myth, you know he was an endearingly silly author with a workaday prose style that just barely served his ragingly romantic imagination. As directed by Hugh Hudson, the movie isn't workaday for a second, with its epic scale and awesome vistas and all. Instead of enhancing the story, though, the niggling details and dignified touches just slow things down.

This would be all right if there were food for thought here: new slants on the ape-man, or fresh situations for him to face. But the plot line of ''Greystoke'' is as venerable as its hero - harking back especially to the 1950s when colorful, big-screen adventures like this were a pop-culture staple, hovering on the respectability scale somewhere between paperback copies of ''From Here to Eternity'' and Classics Illustrated comics.

Of course, the Tarzan myth hasn't been pristine for a long time now. The classic embodiment of the hero, Johnny Weismuller, was nudged aside by more modern interpreters as early as the '50s - I remember one picture that made Tarzan an adopted American visiting Africa as technical adviser on a dam. I'm happy ''Greystoke'' avoids such revisionism and scurries back to the original Tarzan concept, but I wish it showed more energy and less peevishness about decorum.

By contrast, Romancing the Stone has a real sense of humor - not ''amusing moments'' in the ''Greystoke'' vein, but genuine yaks, often at its own expense.

Kathleen Turner plays a popular novelist who leads a boring life until a treasure map falls into her hands, quickly followed by a sinister villain and, in the nick of time, a galumphing hero to guide her through the wilds of Colombia, where the heart of the story takes place.

It's not all fun and innocent romance. There's some nasty violence, rough language, and sex, and Hollywood provincialism shows through in a condescending attitude toward Latin America.

But the filmmakers have devised some clever twists on the earlier films they recall - ''Raiders of the Lost Ark'' and ''Peter Pan'' among them - and they reserve a good share of the derring-do for their heroine, who's a refreshingly far cry from the helpless ladies-in-distress of old. Under the direction of Robert Zemeckis, the action goes limp and perfunctory at a few key moments, weakening the picture's wallop. But it still packs a healthy amount of self-deflating fun.