WASHINGTON — In the largest marine conservation effort in history, President George W. Bush on Tuesday designated what he called "three beautiful and biologically diverse areas of the Pacific Ocean" as national marine monuments.

The areas include the home of a giant land crab, a sunken island ringed by pink-colored coral, and equatorial waters teeming with sharks and other predators and total some 195,274 square miles. Included in the new designation formally announced by Bush at the White House are the Mariana Trench and the waters and corals surrounding three uninhabited islands in the Northern Mariana Islands, Rose Atoll in American Samoa and seven islands strung along the equator in the central Pacific Ocean.

"For sea birds and marine life, they will be sanctuaries to grow and thrive. For scientists, they will be places to extend the frontiers of discovery. And for the American people, they will be places that honor our duty to be good stewards of the Almighty's creation," Bush said.

He said the benefits extend beyond nature, to preserve culturally and spiritually significant sites for native peoples and allow new economic benefits in the territories.

The president also used his announcement to broadly defend his environmental record, which has consistently come under fierce attack during his eight years in office from conservation groups and other critics.

"The new steps I've announced today are the capstone of an eight-year commitment to strong environmental protection and conservation. I know that sounds contrary to the conventional wisdom of many," Bush said.

As evidence, Bush cited moves by his administration to impose the strictest air quality standards in U.S. history and regulations on power plant and diesel fuel emissions; protect millions of acres of wetlands, habitats on farmland and federal forests; clean ocean debris; raise standards on fuel efficiency, lighting and appliances; invest billions in the development of alternative energy sources; and switch the global approach on climate change to one that includes developing economies like China and India.

"We have charted the way toward a more promising era in environmental stewardship," he said. "While there's a lot more work to be done, we have done our part to leave behind a cleaner and healthier and better world for those who follow us on this Earth."

Environmentalists, however, argue that many of his decisions eroded existing protections.

Each location in the new national marine monuments harbors unique species and some of the rarest geological formations on Earth, including a bird that incubates its eggs in the heat of underwater volcanoes and a sulfur pool — the only other one exists on Jupiter's moon Io.

All will be protected under the same status afforded to statues and cultural sites, through the 1906 Antiquities Act. The law allows the government to immediately phase out waste dumping, as well as commercial fishing and other extractive uses.

However, recreational fishing, tourism and scientific research with a federal permit could still occur inside the three areas. The designations also will not conflict with U.S. military activities or freedom of navigation, White House officials said.

It was be the second time Bush has used the law to protect marine resources. Two years ago, the president made a huge swath of the Northwestern Hawaiian Islands a national monument, barring fishing, oil and gas extraction and tourism from its waters and coral reefs. At the time, that area was the largest conservation area in the world.

The three new areas are larger. Still, the designations came with some opposition and fell short in size and scope of what environmentalists had hoped for.

Northern Mariana Islands government officials and indigenous communities initially objected to the monument designation, citing concerns about sovereignty, fishing and mineral exploration.

"These locations are truly among the last pristine areas in the marine environment on Earth," said James Connaughton, chair of the White House Council on Environmental Quality, in a call with reporters Monday. He added that the resources the administration sought to preserve will be fully protected.