Firefighters Tuesday boarded a burning supertanker and began gaining control of a fierce blaze that has left the oil-laden vessel crippled and leaking in the Gulf of Mexico, officials said.

A thick cloud of gray smoke surrounded the superstructure of the 886-foot Mega Borg, replacing the balls of flame and towering columns of black smoke that had been billowing from the Norwegian vessel since an engine-room explosion Saturday."The fire situation has improved," Coast Guard Capt. Thomas Greene said. "It's cooler and you can see this by the gray smoke. The fire in the pump room is out.

"At this point, I'm encouraged by the progress that's been made. We're still not out of the woods yet, and I'm not going to sleep well until it improves more. There's still potential for major problems from (an oil) release."

The Coast Guard also revised its estimate of the amount of oil on the water to less than 2,000 gallons, a fraction of the 100,000 gallons officials estimated earlier. The amount that had spilled from the tanker, which was carrying 38 million gallons of light African crude, was not determined.

Crewmen boarded the tanker to determine if it had cooled enough to be sprayed with flame-smothering chemical foam. Foam spraying had been delayed since Monday because the ship was too hot and crews feared another explosion even if the flames were doused.

Officials speculated it could take as little as an hour to pump the foam into the engine room and other burning areas.

"We're hoping the foam application is a success," said Coast Guard Petty Officer Howard Holmes. If it isn't, "we can't deny the fact that we could be in trouble, but we are optimistic that the foam will work."

Crews Tuesday aimed 10 water streams from five fireboats stationed at the sides of the tanker, and firefighters had placed another water hose on the deck, pointing it toward the burning stern.

Efforts to dissipate an oil leak apparently also were having some success. The oil slick around the ship diminished to 13 miles by 5 miles, Petty Officer Gene Maestas said.

"We're still not completely safe from a major release until the fire is out and the ship is stabilized and brought on an even keel," Capt. Greene said.

Once the fire was extinguished, ships were standing by to begin transferring the remainder of the Mega Borg's cargo of crude. Capt. Greene said that operation could be dangerous because the ship is listing slightly and crews might have to pump water into the holds to keep the vessel balanced.

Earlier Tuesday, the Coast Guard said part of the vessel showed signs of buckling because of the intense 900-degree blaze, the shifting cargo and the continuous stream of water being poured on the hulk. But later, officials said crews at the scene reported no signs of major structural damage.

The tanker caught fire early Saturday while transferring cargo to a smaller vessel. Two of the 41 crewmen died, two were missing and presumed dead and 17 were injured, none seriously.

Little oil spilled at first, but five explosions within 20 minutes Sunday

sent burning crude pouring into the Gulf. By Tuesday, a burning trail of oil that extended for hundreds of feet behind the stricken tanker had diminished to a small pool.

The Mega Borg was carrying more than three times as much oil as was spilled by the Exxon Valdez off Alaska in March 1989 in the nation's worst oil spill. But the oil spilled in Alaska was heavy crude, which doesn't dissipate nearly as rapidly as the light crude aboard the Mega Borg. Also, much of the oil spilling off Texas was being consumed by fire.