CAPE CANAVERAL, Fla.--Initial attempts to locate an explosive satellite booster rocket spotted underwater by sonar failed, and Navy divers intensified their offshore search yesterday for wreckage of the space shuttle Challenger.

The 32,000-pound booster, composed of two solid-fuel rocket motors, was believed to be in an area 18 miles northeast of the launch site, where parts of the shuttle's crew compartment, one of its two solid fuel rocket boosters and other debris have been reported.

"There is plenty of material out there, but they have found nothing identifiable" in dives 100 to 120 feet down late Saturday and early yesterday, said Navy spokesman Cmdr. Arthur E. Norton.

Norton said the 22 divers aboard the Navy salvage ship USS Preserver concentrated their efforts in a zone where "good sonar images" showed the 10-by-17 foot "inertial upper stage" rocket was resting on the ocean bottom.

The Navy focused on the satellite boosters rather than on searching for the shuttle crew compartment or the boosters that propel the spaceship because "they're pretty sure of what they've got there, and it's in relatively shallow water. So, it's a bird-in-the-hand type of situation," Norton said.

"Our people are committed as long as it takes. We may be here months.... The idea is to get the job done."

Navy and NASA officials would not say if there had been any progress in recovering Challenger's crew cabin, rocket boosters or remains from any of the seven astronauts.

Space agency officials would only say that three NASA ships were at sea conducting sonar sweeps and photographing underwater objects with robot subs.

Recovery of the shuttle's right solid fuel rocket booster is particularly important because speculation about the cause of the explosion currently centers on it. Videotape and still photos taken after launch show a plume of fire shooting out from its side toward the external fuel tank, which blew up into a giant fireball.