WASHINGTON » Congress passed legislation yesterday to better protect sharks, creatures that swam the oceans before the age of dinosaurs but that are now being killed by the millions for their fins, a delicacy used in a traditional Chinese soup.

Conservationists called the measure a major step to save a species in trouble. They estimate that 73 million sharks are killed annually to support the shark fin trade and that 30 percent of the world’s species are threatened or nearly threatened with extinction. The loss of too many top predators can disrupt the balance of the populations of other species.

The Senate passed a bill, sponsored by Sen. John Kerry, D-Mass., on Monday, and the House of Representatives passed its version with the same language yesterday, sending it to the president’s desk for his signature. Supporters anticipate that he will sign it.

The legislation requires that sharks caught legally must be landed with fins attached in all U.S. waters. Regulations already had banned cutting off the fins and dumping the bodies in the Gulf of Mexico and the Atlantic, but not in the Pacific. The requirement that the fins remain on the bodies for inspection gives fisheries management officials a clearer picture of how many sharks and what species were caught.

The legislation also closes a loophole in a previous law that allowed fins to be cut off at sea and transferred to nonfishing vessels.

Hawaii banned shark fin soup earlier this year. A state law prohibits the possession, sale, trade or distribution of shark fins.