The tanker Exxon Valdez is most famous for the environmental damage it did when it ran aground on Bligh Reef and spilled millions of gallons of crude oil into Alaskan waters.

The tanker had, however, also caused damage to the environment only hours before that accident. Like thousands of others around the world, the vessel released ozone-causing chemicals into the atmosphere as a routine part of the crude oil loading process.Both state and federal regulators now want these polluting vapors to be recovered. The tanker industry has vigorously fought the regulations, but at an industry conference outside Washington last week, tanker executives were more interested in learning about how they can comply.

"If we have to do it, we'll do it," one executive said.

"I predict in two or three years it will be routine," said Gus

Vonbundgen, deputy secretary at the Louisiana Department of Environmental Quality. "It'll be just another system they (terminal workers) have to operate."

Although vapor recovery systems have been installed in several states, they are still in many senses experimental, and fears remain that they will spark massive explosions.

"There's a great deal more to be learned," said James Seebold, a Chevron Corp. executive and chairman of an American Petroleum Institute task force that seeks ways of preventing explosions.

The recovery systems send vapors being forced out of a ship's cargo tanks back to the land terminals where the vapors are either stored or burned off. Vapors can be highly explosive. A detonation in the vapor piping could travel back to the ship, causing it to explode and spill its cargo into the sea.

"We are giving them (ships and terminals) more opportunity than they used to have to blow one another up," said Mr. Seebold.

The systems are safe, but because they are so new, there is a chance something unexpected could happen, said Chris Clement, an engineering consultant based in Novato, Calif.

Mr. Clement and other industry executives said they do not believe the environmental benefit is worth the safety risks. Only 0.2 percent of the nation's petroleum vapors are released from marine sources.

But environmental officials counter that 0.2 percent is a very significant number. Few large air polluters remain, so the only way to reduce pollution is to go after a lot of smaller polluters, said David Markwordt, a senior environmental engineer with the Environmental Protection Agency. Because marine terminals are clustered close together, in some areas of the country they do contribute a significant proportion of the petroleum vapors in the atmosphere, he added.

Terminal operators will have three or four years to comply with a pending EPA regulation, although state officials already have required systems in New Jersey, California and Texas.

Some states are likely to require vapor recovery during chemical loading also, and the International Maritime Organization is in the process of adding air pollution to its pollution conventions.

In addition to petroleum vapors, the IMO convention will cover ship engine exhaust emissions as well. Ship stack emissions are high in nitrogen and sulfur oxides.

California already regulates sulfur emissions. The EPA is also expected to regulate them, but that is years off.