DINOSAUR ROCK" is the "Tommy" of children's rock- opera, though Michele Valeri and Michael Stein would hardly think of themselves as the Townshend and Daltrey of the third- grade set. Growing out of "The Dinosaur Song" that Valeri recorded with Bob Devlin in 1977, "Dinosaur Rock" is an affecting look back at those giant creatures whose footsteps made the earth tremble.

That initial song is an oldie but goodie, a '50s-style doo-wop number that sounds like an outtake from "Sha Na Na" and ends with a not-so- profundo basso singing "And don't forget the Tyrannosaurus Rex!" The expanded album and the show currently at the Smithsonian's Discovery Theater celebrate as many musical flavors as species: the aforementioned T. Rex gets a mock- heroic western ballad a la Frankie Lane; the "Hadrasaur From Hackensack" sounds not unlike the Big Bopper; those "Leapin' Lizards," the pterosaurs, get a bluegrass treatment. "The Sarapoud Swing" and "The Tiny Little Babies and the Great Big Momma" both sound like Andrews Sisters-style eastern swing, while paleontologist "Professor Jones" yodels and sings to a western swing tune.

The professor is the key link in a story that connects Laurie and John Watson, two vacationing kids, to their pre-history: His sand-sketches, done with dinosaur fossils, spring to life at his yodel and proceed to instruct and entertain the children with illustrative stories about the lifestyles of the large and, unfortunately, extinct. It's all great fun and educational, with most of the vocals shared by Valeri and Stein (the latter a terrific multi-instrumentalist).

There are three ways to enjoy "Dinosaur Rock": tape it, put on your Walkman and walk slowly through the Smithsonian's dinosaur exhibit; sit down with a profusely illustrated dinosaur book and pretend it's a video; or see the show at Discovery Theater (with Pete Kennedy subbing for Stein). Discovery Theater is in the Arts and Industries Building, next to the castle.

The "Dinosaur Rock" record is on the Caedmon label, TC1739. Performances of the show run through November 3; times are Tuesday through Friday at 10 and 11:30 a.m., Saturday at 1 and 3 p.m. Admission is $2.50 for adults, $2 for children. For ticket information, call 357-1500.