The federal government will consider designating areas in the main Hawaiian Islands as critical habitat for endangered Hawaiian monk seals.

The announcement, to be published today in the Federal Register, comes in a response to a petition filed by three environmental groups.

The petition seeks to expand a protected area now comprising the Northwestern Hawaiian Islands to include the beaches and waters of the main islands.

Environmentalists say monk seals in the main Hawaiian Islands are thriving and giving birth while others are dying of starvation, entanglement in fishing gear, shark predation and disease.

Hawaiian monk seals are among the most endangered marine mammals in the world, with fewer than 1,200 remaining. Their population is declining at a rate of 4 percent annually.

The seals are already protected under the Endangered Species Act, Marine Mammal Protection Act and state wildlife laws. But expanding the critical habitat designation would help conservation efforts and provide more funding for research and education, wildlife advocates say.

If designated as critical habitat, any federal activities that may affect the habitat must undergo review.

President Bush in 2006 designated the Northwestern Hawaiian Islands as a protected area. Known as the Papahanaumokuakea Marine National Monument, it is the second largest marine protected area in the world.

The monument covers nearly 140,000 square miles — more than 100 times larger than Yosemite National Park — and is home to more than 7,000 marine species, a quarter of which are found nowhere else on Earth.

The Phoenix Islands Protected Area around Kiribati is the world's largest marine sanctuary at 254,510 square miles.