The blast that crippled the USS Bonefish may have been caused by a battery explosion, and three missing members of the submarine's crew may have died trying to save the lives of their comrades, the Navy's top officer said Tuesday.

The Bonefish remained tethered to a rescue ship as officials waited for toxic gases to clear before starting salvage efforts after the Sunday explosions and fire that injured 22 crewmen.Atlantic Fleet headquarters confirmed Tuesday that the first explosion occurred while the sub was at periscope depth. However, the spokesman refused to comment on speculation that the ship was recharging batteries at the time.

In Washington, Adm. Carlisle A.H. Trost said a battery explosion was a likely cause and said the three missing men might have died while saving the lives of their comrades.

"All three of those individuals . . . were on watch in the ship's control room and were last seen there," said Trost, who is chief of naval operations and a submariner himself.

"So it may well be that they simply ensured that everyone got clear and they themselves didn't make it."

Relatives of the missing sailors, meanwhile, maintained vigils.

"We still have a little ray of hope," said Joyce Lindgren, mother of Petty Officer 3rd Class Marshall T. Lindgren of Pisgah Forest, N.C. "When he enrolled in the Navy I gave him to the Lord and I have to have trust in him now."

The 30-year-old submarine, one of the Navy's last diesel-electric subs, was participating in training exercises Sunday in the Atlantic about 160 miles off the coast of Florida when it was rocked by a series of explosions.

At least one blast occurred in the battery compartment, and fire broke out in the forward battery compartment, said Lt. Cmdr. Aaron Long, spokesman for the Atlantic Fleet headquarters in Norfolk.

The crew brought the sub to the surface, and its captain, Cmdr. Mike Wilson, ordered it abandoned because of the dense smoke and toxic fumes.

Of the 92 officers and crew members, 89 were taken aboard the frigate USS Carr and aircraft carrier John F. Kennedy, which were involved in the exercises. The ships were unable to find the three others, and officials were uncertain whether they were aboard the vessel or in the water.

The Bonefish was afloat Tuesday alongside the submarine rescue ship USS Petrel. Salvage workers were to board the sub once experts decided it was safe, but Navy officials were unsure when that would be, Long said.

Long refused to say what types of toxic gases might be present or what caused the explosions.

The Virginian-Pilot of Norfolk reported Tuesday that the first explosion occurred at periscope depth, leading to speculation that the ship was recharging its batteries via a generator drawing air through a snorkel raised with the periscope.

Fleet spokesman Lt. Fred Henney confirmed Tuesday morning that the first explosion did occur at periscope depth, less than 70 feet below the surface, but would not comment further.

Trost said "battery explosion is the best information that we have" as to the cause.

The salvage ship USS Hoist from the Little Creek Amphibious Base in Norfolk was expected to join the Petrel at the scene.

On Monday, injured sailors were taken by helicopter from the Kennedy to the Naval Hospital in Jacksonville, Fla. Twenty were held for observation, and two were in serious but stable condition in intensive care, suffering from smoke inhalation.