Two wildlife-protection groups announced today they have filed a federal lawsuit to restore safeguards for endangered North Atlantic right whales, humpbacks, and fin whales.

The groups, Defenders of Wildlife and The Humane Society of the United States, said they filed suit yesterday against the National Marine Fisheries Service because the agency delayed new protection rules for six months and at the same time allowed old rules to expire. The delayed rules would have required lobstermen in Maine and other New England states to switch from using floating lines to connect traps to using sinking lines that are less likely to snag passing whales.

Maine's lobster industry has resisted the switch to sinking lines, saying the lines would snag on the rocky sea floor here. The fisheries service agreed this month to delay the requirement from October until April, saying there are fewer traps in the water during the winter and less risk to whales.

The wildlife groups said the gap in protections comes after years of delay and will put whales at increased risk for the next six months. The suit says the delay violates the Marine Mammal Protection Act, the Endangered Species Act and other conservation laws, and asks the federal district court in Washington, D.C., to force the agency to reinstitute protections.