For several years, Americans have been warned not to eat swordfish more than once a week because of the potential for mercury poisoning. Now, they may have a reason not to eat swordfish at all: Population levels are in serious decline, and unless measures are taken, there may not be a commercial swordfish industry in 10 years.

Concerned about the potential loss of swordfish, some top New York restaurants have pledged not to serve it this year. They've joined a campaign called Give Swordfish a Break, intended to draw attention to the fact that the North Atlantic, the source for most East Coast markets, has been seriously overfished. (Pacific swordfish have also been overfished but not to the same extent.)Who could possibly oppose such a campaign? The National Marine Fisheries Service for one. That federal agency, which regulates commercial fishing within 200 miles of coastal waters, acknowledges that swordfish are in decline but says there is no need for Americans to stop eating them entirely, because the government is already taking steps to increase the population.

Rebecca Lent, chief of highly migratory species in the management division of the fisheries service, said that the restaurants' campaign "penalizes U.S. fishermen who are already abiding by the law."What is needed, she said, is better compliance from other countries that catch significant amounts of swordfish.

So many swordfish are being caught now that many do not grow to full size. In the early part of the century, the average weight of a swordfish when caught was around 300 pounds; today it is 90 pounds. International regulations prohibit fishermen from keeping any swordfish weighing less that 33 pounds.

Before the 1960s, swordfish were caught by harpooning; today they are caught on a 40-mile fishing line with hundreds of hooks that catch any fish that takes the bait, including thousands of swordfish that do not meet the weight requirement. Some 40,000 undersized swordfish are discarded each year by the American boats alone, and almost all of those fish die in the process. The majority of swordfish caught, including those of legitimate size, are too young to have reproduced, further reducing future populations.

Pollution continues to be a problem. Swordfish are contaminated with mercury that washes into the ocean after being produced by industrial processes and the burning of fuels. The Food and Drug Administration advises that swordfish be eaten only once a week (once a month for pregnant women) to limit the level of exposure to mercury.

Most people who buy swordfish at the fish counter probably never stop to think about why the steaks keep getting smaller and smaller.

"People are not aware of how polluted and fished-out the oceans are," said Nora Pouillon, the chef and a partner in Restaurant Nora and Asia Nora in Washington. She has written to fellow chefs asking them to join Give Swordfish a Break.