Barack Obama

WASHINGTON — White House said on Tuesday that President Barack Obama announced plans in preserving the world by banning drilling, fishing and other activities in a massive stretch of the largest ocean, the Pacific Ocean, but could run into opposition from the fishing industry and lawmakers are worried about the president’s use of executive power.

The president announced his plans via video message at an oceans conference hosted by the State Department.

“We can protect our oceans for future generations,” Obama said, vowing to use his “authority as president” to protect “some of our most precious marine landscapes.”

Obama warned that carbon pollution is making the world’s oceans more acidic and pollution is threatening the marine life. He also noted that overfishing could wipe out the entire species.

“If we ignore these problems, if we drain our oceans of their resources, we won’t just be squandering one of humanity’s greatest treasures, we’ll be cutting off one of the world’s major sources of food and economic growth, including for the United States. We cannot afford to let that happen.”

The Washington Post reported that Obama is looking at expanding the preserve, from almost 87,000 square miles to nearly 782,000 square miles. The monument, created by President George W. Bush just before he left office in 2009, includes seven islands.

‘‘These tropical coral reefs and associated marine ecosystems are also among the most vulnerable areas to the impacts of climate change and ocean acidification,’’ the White House said in a statement.

The practical effect of the expanded marine sanctuary could be modest. The Philippine Daily Inquirer recounted that a very little commercial fishing is conducted in the waters Obama is seeking to protect, and there are no signs that drilling in the waters is imminent at the present. But conservation groups said it was crucial to take proactive steps to prevent such activities going forward.

Moreover, Fox News reported that Obama also plans to create a government program to combat black market fishing and seafood fraud, in which seafood products are mislabeled to hide their origin. The White House said 20 percent of the wild marine fish caught each year are part of the black market, at a cost of $23 billion to the legitimate fishing industry.

‘‘President Obama’s announcement is a historic step forward in the fight against seafood fraud and illegal fishing worldwide,’’ said Beth Lowell of the conservation group Oceana. ‘‘This initiative is a practical solution to an ugly problem and will forever change the way we think about our seafood.’’

Obama, in his public comments, indicated the significance was partially symbolic. By taking the lead on ocean conservation, the U.S. can encourage the rest of the world to protect resources for future generations.

“For this effort to succeed, it has to be bigger than any one country,” the president said.