By JULIAN E. BARNES

WASHINGTON—A key Senate Democratic leader said he won’t push for a vote on the politically divisive Law of the Sea treaty before the presidential election in November, but will seek to line up support for ratification in the coming months.

Sen. John Kerry (D., Mass.), chairman of the Senate Foreign Relations Committee, opened a series of hearings on Wednesday, inviting Secretary of State Hillary Clinton and Defense Secretary Leon Panetta to argue for ratification of the long-stalled pact.

Agence France-Presse / Getty ImagesA Philippine soldier in Masinloc, 140 miles from the disputed Scarborough Shoal area in the South China Sea.

Mr. Kerry said he hoped to avoid ensnaring the treaty, which is opposed by some conservatives, in the presidential election campaign.

“I do not want this treaty to become victim to that race or the politics of the moment,” Sen. Kerry said. “We will wait until the passions of the election have subsided before we vote.”

Obama administration officials want ratification this year, but said a vote could be held in the lame-duck period following the election.

The treaty sets international navigation rules, which U.S. Navy officials consider important and which business groups argue are critical for exercising rights to mine the ocean floor or explore for oil in the Arctic.

Advocates of ratification warn that if the U.S. doesn’t join the pact, other nations will be able to shape the rules for exploring the ocean floor, without the U.S. input.

Opponents, including the Heritage Foundation, a conservative think tank, have suggested that joining the treaty would cede too much control of the seas to the United Nations and other international bodies.

In past years, many Republicans on the Foreign Relations committee have supported the treaty. But Steven Groves, a scholar at the Heritage Foundation, said the hearing showed strong opposition among most of the Republicans on the committee. “Opposition to the treaty isn’t leveling off or declining, it has been growing,” he said.

Democrats are hoping Sen. Richard Lugar (R., Ind.), who was defeated in a primary election this month, will push his party to embrace the treaty as part of his Senate legacy.

Joining the treaty, said Mrs. Clinton, will ensure the U.S. can defend its interests, and secure claims to oil resources and other natural resources on the continental shelf.

The treaty was drafted in 1982. Then-President Ronald Reagan declined to send it to the Senate for ratification because of concerns over seabed mining provisions. Those provisions were modified in 1994, and Presidents Bill Clinton and George W. Bush both supported ratifying the pact.

Wednesday’s hearing demonstrated the continued skepticism among Republicans toward the treaty. Sen. Robert Corker (R., Tenn.) said he hadn’t made a decision on ratification, but questioned how the Obama administration, which has been critical of the oil industry, could cite oil exploration in support of ratification. “My antennae are up,” he said.

Other Republicans said they suspected the treaty would impinge on American sovereignty, for instance, by forcing the U.S. to agree to international emissions controls to comply with treaty provisions on pollution over the oceans.

Sen. James Risch (R., Idaho), argued the treaty’s royalty-sharing provisions would essentially tax companies exploring the seabed, sending proceeds to developing nations and ceding American taxing authority to the United Nations. “My problem is with sovereignty,” he said. “If we give up one scintilla of sovereignty the country has fought for… I can’t vote for it.”

Sen. Jim Inhofe (R., Okla.) predicted the U.S. would have to give up more than $70 billion in royalties. “For the first time an international organization, in this case the United Nations, would have taxing authority over the U.S.,” Mr. Inhofe said.

Mrs. Clinton insisted the treaty didn’t cede American sovereignty, and said there are other examples of the U.S. providing money to international bodies, such as the U.N.’s telecommunications agency. “No country is in a position to gain more from the Law of the Sea Convention than the United States,” she said.

In her opening testimony, she attacked critics who have argued the treaty gives the U.N. too much power and creates a global tax that could go to countries that support terrorism. Ratifying the treaty, Mrs. Clinton said, would give the U.S. a veto over every decision on where royalties from the seabed are distributed.

“If we don’t join the convention, our companies will miss out on opportunities to explore vast areas of the continental shelf and deep sea bed,” she said. “If we do join the convention we unlock economic opportunities worth potentially hundreds of billions of dollars for a small percentage royalty a few years down the line.”

Military leaders are keen to join the treaty. They are increasingly concerned about China’s interpretation of the treaty and its arguments that the U.S. shouldn’t have the right to conduct military exercises within Beijing’s exclusive economic zone.

Mrs. Clinton said joining the treaty would allow the U.S. to fight for open access to the South China Sea and elsewhere.

“There are many in the world who hope we never are a party. They can go and plot the way forward, set the rules, enforce them as they choose, putting us further and further at a disadvantage,” Mrs. Clinton said.

Mr. Panetta said ratifying the treaty would help secure American navigation rights in the Arctic, which because of the melting of northern ice is opening up as a navigation route.

—Keith Johnson and Brian Spegele contributed to this article