** 1/2 "The Three Worlds of Gulliver."
RCA/Columbia. $69.95. 1960.
Until the special effects start, this adaptation of "Gulliver's Travels" is dull, flat and obvious--even though writer-director Jack Sher, for once, has decided to include both the gigantic Brodbignagians and the minuscule Lilliputians on Gulliver's itinerary. But, though the writing and acting never improve much, effects-master Ray Harryhausen gives the movie real magic once he's given his head. And Bernard Herrmann has supplied a score as stirring as any he wrote for Alfred Hitchcock. For children, the rating is raised to three checks.