“The U.S. government has been firmly behind protecting its citizens from shipping pollution through negotiations with the IMO both through the Bush administration and the Obama administration, so it’s not a partisan issue,” said David Marshall of the Clean Air Task Force, an advocacy organization.

Some activists in Charleston, where cruises dock year-round, are fighting the industry on air and noise pollution.

The EPA estimated that when the emissions-control plan is fully implemented, as many as 31,000 premature deaths per year will be prevented. Cleaner air would mean fewer emergency-room visits for people with asthma and other lung diseases. The new standards also would reduce acid rain on coastal forests, lakes and crops.

The agreement requires large ships to drop the sulfur content of their fuel from 15,000 parts per million to 10,000 parts per million in August, and to 1,000 parts per million in 2015. It allows alternative approaches that get equivalent amounts of emission reductions, such as exhaust scrubbers.

Cleaner fuel costs more than the sulfur-rich bunker oil that ships use today. The EPA estimated that the price increase on a seven-day Alaska cruise would be 1.5 percent to 6 percent.

The online trade publication Sustainable Shipping reported that cruise companies don’t want to pass on too much of the cost for fear of reducing customer demand, so the industry’s profits might decline. A study for the industry projected fewer cruises to Alaska, Canada and the Caribbean, as well as job losses.

Miami-based Carnival Corp., the world’s biggest cruise company, reported $1.9 billion in profits last year. Carnival spokesman Aly Bello-Cabreriza declined to comment and referred questions to the industry lobby group, Cruise Lines International Association. Other cruise companies also declined to comment.

Cruise Lines International Association has proposed a complicated emissions-averaging plan that would allow ships to continue to burn high-sulfur fuel sometimes. An advantage would be lower costs, the association’s director of environmental and health programs, Charles Darr, said in an April PowerPoint presentation.

The method would allow a ship to vary its emissions based on such issues as weather conditions and location. Ships would switch to cleaner fuels near heavily populated areas.

Officials of the EPA and the Coast Guard opposed the Cruise Lines International Association plan in a letter March 12 to International Maritime Organization Secretary-General Koji Sekimizu.

“After analysis, we believe the cruise lines proposal is unacceptable because it would result in overall higher emissions and doesn’t meet public expectations of uniform delivery of health and environmental benefits for citizens of the United States,” wrote Jeffrey G. Lantz, the Coast Guard’s director of commercial regulations and standards, and Margo Tsirigotis Oge, the director of the EPA’s office of transportation and air quality.

Democratic Sens. Bill Nelson of Florida and Patty Murray and Maria Cantwell of Washington state also have written to the EPA asking it to consider the industry’s views. Nelson was the top Senate recipient of cruise-ship industry donations last year. He received $19,200, according to the Center for Responsive Politics, a nonpartisan research group.

A bipartisan group of House members, led by John Mica, R-Fla., the chairman of the House Committee on Transportation and Infrastructure, sent the EPA a letter of support for the cruise line association’s plan in March.