The explosion in a 16-inch gun turret aboard the battleship USS Iowa may have been caused by red-hot debris from a firing left in the breech, a former commander of the ship said Thursday.

And, though certainly not an expert, a Utah man who served on the USS Iowa independently suggested the same cause. (See story on A2.)Capt. Larry Seaquist, the Iowa's commanding officer until last May, refused to speculate on the exact cause of the accident that left 47 sailors dead.

But he told reporters at a Pentagon briefing that an air system to clear debris from the breech must be operated manually, raising the possibility that the procedure was overlooked before fresh gunpowder was loaded into the gun during a firing exercise.

"It seems from the reports that those powders exploded," Seaquist said.

"We simply do not know what caused that powder to go," he said. "The early reports are that it was up in that gun room," immediately behind the gun breeches.

Other Pentagon sources, who spoke on condition they not be further identified, said that the lone officer and the senior enlisted man stationed in the turret were killed in the explosion. They are normally stationed in a small office at the rear of the turret, directly behind the gun house where the charges are loaded.

Their deaths were strong evidence that the explosion occurred in the gun room.

The battleship arrived off Roosevelt Roads Naval Station, Puerto Rico, Thursday, carrying the bodies.

Navy officials said the bodies of those killed in Wednesday's explosion inside the turret holding three 16-inch guns were being brought ashore by helicopter and then would be flown to a military mortuary in Dover, Del.

The Pentagon put the death toll at 47 and said other crew members were accounted for. Earlier, spokesmen had said the death toll could be higher.

Ten to 12 crew members suffered minor injuries. "Most of these . . . were in the firefighting party," Pentagon spokesman Fred Hoffman said at a briefing this morning. They were treated aboard ship and were back at work Thursday, the Navy said.

The explosion occurred during a gunnery exercise while the 46-year-old ship was on maneuvers about 330 miles northeast of Puerto Rico.

Meanwhile Defense Secretary Richard Cheney, en route home from a NATO meeting in Brussels, said "we have no eyewitnesses to what actually transpired."

"I've been told in reports today that everyone who was in the turret at the time of the explosion was killed," Cheney said, apparently referring to the swiveling gun house at the top of the turret, rather than the mechanical compartments and ammunition magazines below it.

Under questioning by reporters, Seaquist said one possible cause of the explosion was debris left in the breech from a previous firing.

To clear the breech of such debris, he said, a sailor must manually activate a one-inch tube containing air pressurized at 3,000 pounds per square inch, and then visually inspect the breech.

"It ejects the gases out of the muzzle of the gun," he said.

"Each of these men is well-trained and formally qualified to do this," he said, and they drill regularly.

The turret and the ship are constructed of thick steel and are designed in such a way that a fire or explosion in one compartment of the turret will not spread to other sections, ignite powder magazines and spread the damage.

"This gun, the Mark VII, 16-inch 50 gun remains the finest naval gun in the world. It was the pinnacle of gun design art, and it is still a front-line system," Seaquist said.

"It was designed specifically to contain this kind of damage, to limit the cascading effects," he said, referring to explosions that occurred aboard ships of earlier designs.

At some point during the accident Wednesday, the crew flooded the turret, activating an overhead sprinkler system that sprays the compartments with pressurized salt water while still allowing sailors to scramble through exit hatches.

A complement of 74 sailors normally work inside each turret, said Seaquist.

Pentagon spokesman Fred Hoffman said "the reports coming in from the ship indicate that it was fully manned at the time of the firing. There were survivors (in the turret)."

Hoffman said he could not say whether all of those killed were inside the turret at the time of the explosion.

To launch a 1,900-pound projectile from the 62-foot-long barrels, a team of sailors packs six gunpowder canisters weighing 110 pounds each into the breech, Seaquist said.

The black gunpowder, a total of 660 pounds, is ignited, propelling the shell from the barrel at a speed of 1,500 miles an hour, he said.

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(Additional story)

Iowa facts

-Despite two wars and patrol duty last year off the Persian Gulf, the USS Iowa has been struck only once by enemy fire.

-A World War II hulk of a battleship, it has wooden decks and the rare added amenity of a bathtub.

-The ship has nine 16-inch guns that can hurl shells as heavy as a small car a distance of 23 miles.

-Only three other ships in the Iowa's class have cannon that large.

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(Additional story)

Call about crew

Here is the telephone number set up to handle inquiries about the crew of the USS Iowa: 1-800-368-3202 or 1-800-523-2975.

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(Additional Story)

Partial list of dead

Here is a list of sailors the Pentagon says were killed in the explosion Wednesday aboard the battleship USS Iowa. Other names will be released as next of kin are notified.

-Tung Thanh Adams, Alexandria Va.,

-Robert Wallace Backherms, Ravenna, Ohio.

-Dwayne Collier Battle, Rocky Mount, N.C.

-Pete Edward Bopp, Levittown, N.Y.

-Phillip Edward Buch, Las Cruces, N.M.

-Leslie Allen Everhart, Jr., Cary, N.C.

-Robert Kenneth Morrison, Jacksonville, Fla.

-Jack Ernest Thompson, Greeneville, Tenn.