How does an adult reviewer approach a movie such as ``Big Top Pee-wee''? Very carefully. If you lambaste it as an entertainment aimed at the 5-year-old audience, you might be accurate. But you could also be accused of being a kill-joy and a fogy. If you try to compare it with the innocent comedy of the silent screen, you might also score some points. But you could also be accused of hunting for gold in a pile of dross. So here goes. ``Big Top Pee-wee'' is a clever piece of pure entertainment conceived by Paul Reubens and executed by Pee-wee Herman, who are the same person. Those who loved ``Pee-wee's Big Adventure'' will adore this one. The story begins with Pee-wee waking up on the most antiseptic farm in the world. Everything is sunny and bright, matching Pee-wee's personality. The animals sleep on mattresss and eat flapjacks at a picnic table. Pee-wee's greenhouse is a wonder. With his magic food supplements, he can grow anything. Even hot dogs. Pee-wee's constant companion is Vance, a pure-white pig. Vance talks. With a charity seldom seen in comedians, Pee-wee gives Vance most of the punchlines. But then, how are you going to upstage a talking pig? Every day Pee-wee is scheduled for a sandwich lunch with his heartthrob, the local schoolmarm (Penelope Ann Miller). For such a shy man, Pee-wee can be aggressive. He throws his body on top of the schoolmarm, who resists him because the schoolkids are watching. And taking snapshots. Then the circus comes to the farm. A new set of animals are roaming the acres, as well as exotic circus people, such as the Italian aerialist (Valeria Golino), with whom Pee-wee falls in love. The townspeople object to having the circus in their midst, providing a modicum of conflict to the script. Centerstage at all times is Pee-wee Herman, a man with a squeaky voice, tight suit and white socks. He is, in the end, an endearing character, guileless yet savvy. He wears well, despite the inane circumstances in which he finds himself. Kris Kristofferson as the circus boss lends strength, though his three-inch wife (Susan Tyrell) stretches fantasy too far. Randal Kleiser directed in a straightforward fashion. Only one sequence is truly hilarious, and that is borrowed from Alfred Hitchcock. When Pee-wee finally makes love with the aerialist, we see a train entering a tunnel (``North by Northwest'') and skyrockets exploding (``To Catch a Thief''). ``Big Top Pee-wee'' was produced by Reubens and Debra Hill, and written by him and George McGrath. The rating is PG, perhaps for sexual innuendo. Running time: 87 minutes.