A cutline yesterday incorrectly identified Sen. Bob Packwood (R-Ore.) as a Democrat.

The United States and Japan have reached an agreement that will allow Japan to ignore an international moratorium on commercial sperm whaling without the threat of severe economic sanctions on its rights to fish in American coastal waters.

The accord has prompted sharp criticism from Sen. Bob Packwood (R-Ore.), who sponsored the legislation that imposed the sanctions, and from several environmental and animal-welfare groups, which have filed suit to block implementation of the the agreement.

The critics fear that if Japan is allowed to violate the moratorium without facing sanctions, then other whaling nations, specifically Brazil and Norway, will follow suit when a ban on all kinds of commercial whaling takes effect in two years. They contend the agreement will allow Japan further to deplete the sperm whale population, and that it amounts to an about-face by the Reagan administration, which previously had supported the ban and sanctions to enforce it.

The agreement, details of which had not been released as of yesterday, would allow Japanese fishermen to continue hunting for sperm whales for several years despite a ban imposed by the International Whaling Commission in 1982. The ban on sperm whaling in the North Pacific was viewed as a first step toward the worldwide moratorium in 1986.

A. Joseph LeCovey, director of public affairs for the National Oceanic and Atmospheric Administration, yesterday described the agreement as a "tentative understanding. It was finalized at a Friday morning meeting and was just being put down on paper Friday afternoon. If they the Japanese take certain actions, they can avoid certification" and sanctions, he said.

LeCovey said the details should be available today or Wednesday, after both sides have had a chance to review the language of the agreement.

Japan had lodged a formal objection to the ban, a technical way in which countries can exempt themselves from an IWC ruling.

But under an amendment that Packwood sponsored in 1979 to the Fishery Conservation and Management Act, the Commerce Department is required to impose tough economic sanctions on any nation that "diminishes the effectiveness" of the IWC.

Under that amendment, Japan would lose its rights to half its allocation of fish in U.S. waters. But Reagan administration officials, eager to avoid an economic showdown with a key ally and trading partner over the whaling issue, began negotiating a compromise that would allow Japan to ignore the ban and avoid the sanctions.

Packwood and the conservation groups have said the agreement is illegal. "It the Packwood amendment is absolutely mandatory, not discretionary policy," Packwood said in a news release earlier this month.

"It leaves no wiggle room or gray area in which representatives of our government can negotiate with the Japanese or any other foreign power to take sperm whales."

When Japan first announced its objections to the ban in late 1982, Mike Mansfield, the U.S. ambassador in Tokyo, hand-delivered a letter to Japanese Foreign Minister Yoshio Sakurauchi, warning of the potential economic sanctions. And as late as last July, Commerce Secretary Malcolm Baldrige wrote Packwood that "any government that chooses to ignore the commercial whaling moratorium . . . should be prepared to accept the consequences of this non-compliance."

For the Japanese, the issue is both emotional and highly political, because whales have long been a staple food product and whaling has long been a part of the country's history.

The Financial Times of London has reported that a whaling ban would mean a loss of $50 million in primary whale products to Japan, and an added $150 million in secondary whale products such as oil extracts and cosmetics. The newspaper estimated that as many as 14,500 jobs could be lost.

The environmentalists prefer to emphasize that by their estimates, only 130 Japanese fishermen still hunt for sperm whales.

By contrast, Japan's fishing industry earns an estimated $500 million each year from its take in U.S. waters.

A coalition of nine environmental and animal welfare groups last week filed suit against Baldrige and Secretary of State George P. Shultz in U.S. District Court here, seeking to block the agreement and force Baldrige to impose the sanctions.

"What we're trying to prevent is the formalizing of that agreement," said Mark Cheater, wildlife legislative director for the environmental group Greenpeace.

"It sets a very dangerous precedent," Cheater said. "If this agreement goes through, the Norwegians will be back, the Brazilians will want something similar. It will basically set up a chain reaction that's going to put the future of the IWC as a regulatory body in serious jeopardy."

The IWC was created in 1946 under an international convention to regulate whaling. Over the past decade, as the whale population has declined dramatically, the commission has approved several measures, including restrictions on the number of whales that can be taken from particular waters and restraints on some killing methods. But the IWC has no enforcement powers, and any nation that officially objects to an IWC ruling removes itself from the commission's jurisdiction.

Patricia Forkan, a vice president of the Humane Society of the United States, said, "We don't think the government has a basis for selling out the whales . . . . I think it spells disaster for the IWC. It could undermine the authority of the IWC and that could really rip the fabric of that organization."

The agreement, and the suit to block it, came as Greenpeace members in Tokyo reported that the first two sperm whales of this new season have been brought into a Japanese port over the weekend. The returning whalers were met at the port by Greenpeace members holding placards, in Japanese and in English, which read: "Stop Pirate Whaling."