All those Americans who were thinking they might like to try life under a totalitarian dictatorship for a while will certainly think again after they see "James Clavell's The Children's Story," a ludicrously simplistic and amateurish fantasy that comes out foursquare and fourscore for Our Way of Life.

Surely there must also be a sneaky plug for oil-depletion allowances hidden in there somewhere -- else why should Mobil make this dull trinket an offering of its syndicated Mobil Showcase Network (tonight at 8 on Channel 5), design a fancy-shmancy logo for it, throw a big dinner party in L.A. for it, and otherwise undertake ze big promotional splash? All for a 30-minute film with a script that any halfway-decent high school English teacher would reward with a big fat F.

Clavell's cautionary fable (less sophisticated than those ringing endorsements of unlimited oil company profits Mobil loves to run as commercials) is set in a grade school classroom sometime in the future when, it says on the screen, "THEY have just conquered us." A dear, sweet old granny-type teacher (Mildred Dunnock, appearing for about two seconds) gets her walking papers and a cold, crafty new teacher (Michaela Ross) stalks in.

And what does the new teacher do? Oooo, she's a bad 'un. She discredits the Pledge of Allegiance, mocks the existence of a God, and cuts up an American flag with a scissors. Cunningly, with candy yet, she wins over the hearts and minds of the pliable tots, lecturing them with phrases like "each according to his age group, each according to his need." This babe makes Tokyo Rose look like Suzie Subtle. The film ends with the ominous tick-tick-tick of a clock on the wall. Certainly this will give second thoughts to all those Americans who've been considering breaking into a communist country, or who plan to support Ayatollah Khomeini for president in 1984.

The real marvel of it all is Clavell's agent, or Clavell's ego, or both. They have parlayed the kind of script that wouldn't have made it past first cut on "Twilight Zone" into a big Mobil blowout. Clavell's name is not only part of the title: His credit reads, "Author, writer-producer-director." And guess who Michaela Ross is. She's Clavell's daughter, a vaguely pretty model who is less impressive an actress than Baretta's old cockatoo. Television really is a haven for people who have no shame.