If ever there were an environmental threat that seemed ripe for a legislative remedy, it is the shipment of oil. The explosions this weekend aboard the Norwegian tanker Mega Borg in the Gulf of Mexico is only the latest in a spate of shipping mishaps that has soiled beaches and wildlife from New York Harbor to Alaska's Prince William Sound.

But despite the widespread public outrage that has accompanied television images of oil slicks and dying sea otters, Congress is still wrangling over comprehensive oil spill legislation introduced in the aftermath of last year's Exxon Valdez disaster.

The legislative bottleneck is testament to both the complexity of the issue and the continued influence of the oil industry in Congress, particularly among lawmakers from energy-producing states.

"The fact that Congress hasn't adopted these measures is outrageous," said Lisa Speer, senior staff scientist with the Natural Resources Defense Council. "Every day that passes without oil spill legislation means that more oil pours into the nation's coastal waters."

Competing versions of the oil spill bill passed both the Senate and House late last year, and the measure is currently in conference.

Nearly everyone seems to agree that existing liability limits for oil companies are too low, that federal response capabilities are inadequate and that oil tankers should be more accident-proof than they are today.

But conferees have been unable to resolve key differences over the amount of liability exposure and whether to require the industry to replace its tankers with double-hulled versions -- a step one oil company, Conoco, has already agreed to take on its own. The oil industry has argued that an across-the-board requirement for double hulls would be too costly, and backs instead a proposal to delay action pending a National Academy of Sciences review.

Backers of tougher federal legislation say the need was graphically demonstrated by the Exxon Valdez spill of nearly 11 million gallons in March last year. Not only was spill-fighting equipment late reaching the grounded tanker, but it proved woefully inadequate for the task. An internal Coast Guard study subsequently concluded that if the ship had been equipped with a double bottom, as much as 60 percent of the spilled oil could have been saved.

Also of concern to environmentalists and their congressional allies is the liability limit for oil tankers involved in spills -- now generally capped at $68 million per shipper -- and the lack of a sizeable federal trust fund to cope with spills in the event that an oil company does not cooperate. Exxon spent about $2 billion cleaning up after the Exxon Valdez spill.

Under the legislation in conference, liability limits would be raised several-fold and a trust fund to provide $1 billion per spill would be created with revenues from a 5-cent-a-barrel oil tax. A Gulf of Mexico oil spill "strike force" would be created to cope with emergencies such as the Mega Borg explosions, in which firefighting equipment had to be flown in from as far away as Rotterdam.

But a major sticking point has arisen over a provision that would allow states to seek higher damage awards than those allowed by the federal law -- a provision that could increase oil companies' exposure dramatically in cases of catastrophic spills. Some conferees, echoing the oil industry, have argued that the United States should ratify proposed international protocols setting uniform liability standards, which would preclude higher state damages.