The United States and Canada announced a landmark agreement yesterday on salmon fishing in the Pacific Ocean, a pact designed to end a bitter, decades-long dispute over the harvest of fish whose epic migrations ignore national boundaries and have sometimes brought competing fishermen to the brink of violence.

Hailing the agreement after years of difficult negotiations and frayed relations between their neighboring countries, Secretary of State Madeleine K. Albright and Canadian Foreign Minister Lloyd Axworthy said in a joint statement that the new arrangement "represents a victory for all those on both sides of the border interested in salmon conservation and the long-term viability of our salmon industries."

At the heart of the accord is the establishment of a new regime for setting fishing quotas under the 1985 Pacific Salmon Treaty that is flexible and based on how abundant the fish are, instead of fixed annual limits.

The new technique, first used several years ago by Alaska over the strenuous objections of Canadian and tribal interests, is designed to respond to often large fluctuations in runs of the five species of salmon in the north Pacific. In force for 10 to 12 years, depending on the fishery, the new regime will allow larger harvests in years of abundance and smaller ones in lean years, but overall will likely reduce the catch by 5 percent to as much as 50 percent in some stocks.

The agreement is expected to reduce the U.S. share of the total Pacific salmon harvest to 16.5 percent from a historical average of 20.5 percent.

A second critical component is the establishment of two funds, to be administered jointly by Canada and the United States, that would be used to assist in the recovery of threatened salmon stocks and in improving fisheries management. The Clinton administration has pledged to seek $140 million from Congress to finance those efforts over several years. Canada will not contribute to the funds, a tacit recognition that it is owed compensation because American fishermen, particularly in Alaska, have for years taken more than their fair share.

Lloyd N. Cutler, a former White House counsel who entered the talks as a special administration representative, said, "We are confident that there will be strong bipartisan support to honor this [financial] commitment."

The agreement, which goes into effect immediately, aims to fulfill the promise of the 1985 treaty, which sought to prevent overfishing by assigning catch limits to each nation based on what percentage of the overall population came from each country's rivers. But talks to implement the treaty broke down in 1992 when Canada walked out amid continuing disagreements over interpretation and scientific issues.

The dispute has been unusually difficult to resolve in part because salmon that are born in U.S. or Canadian rivers commingle after migrating to international waters in the northern Pacific and often pass through coastal waters of the other country before returning home to spawn. In addition, there are many competing interests, including fishermen from two nations, three U.S. states and 24 Indian tribes.

Two years ago, the dispute boiled over into a volatile confrontation in Prince Rupert, British Columbia, when Canadian fishermen, outraged by what they said was poaching by Alaskans, blockaded an Alaskan ferry and threatened to block the Alaska highway that passes through their province.

A number of factors -- economic, environmental and political -- contributed to breaking the political logjam.

With many Pacific salmon stocks in decline because of overfishing, climatic changes and habitat degradation, and with abundant farm-raised salmon driving down prices for wild salmon, the pie over which everyone was fighting was getting much smaller very quickly. The value of the overall Pacific salmon fishery is half what it was just a few years ago, when fishermen at the dock received about $650 million for their catch.

As one Canadian diplomat said: "It's a lot easier to get agreement on how to share the misery than it is on how to share in abundance."

At the same time, senior political leaders in both countries, alarmed by both the decline in salmon stocks and the price being paid in the relationship between Canada and the United States, gave the talks and the issue renewed importance. For example, Canada's new fisheries minister, David Anderson -- an avid fisherman and environmentalist -- began taking on British Columbia Premier Glen Clark and his fishing union allies. He unilaterally imposed new conservation measures such as a virtual ban on all fishing for coho salmon, and Canada undertook a $260 million program to preserve habitat, improve research and buy up fishing licenses. Similar dramatic conservation steps have been undertaken in the United States with the Clinton administration extending endangered species protections to numerous salmon runs in the Pacific Northwest.

In essence, top negotiators from both countries agreed to reposition the issue from one of dividing a rapidly shrinking pie more equitably to conservation. "For years, politicians and officials from Canada and the United States have been locked in an endless and fruitless argument over who will catch the last few fish," Anderson said in a recent speech. "Putting fish first means putting an end to all that."

Clark, piqued at having been left out of the negotiations, criticized the treaty, saying it "entrenches . . . the right of Alaskans to catch more [British Columbian] salmon than ever."

At the same time, Clark said, Canadians are prohibited from catching any coho salmon, while Alaskans are allowed to catch them over the next decade.

Oregon Gov. John Kitzhaber (D) hailed the accord as a "victory of diplomacy over conflict, a victory of regionalism over parochialism."

Dale Kelley, executive director of the Alaska Trollers Association, said the agreement will likely mean that the 1,300-plus trollers who fish for chinook salmon will have to wait even longer to reap the benefits of a 100,000-fish cutback they took under the treaty in 1985.

"Ninety-nine percent of the stocks in our fishery are healthy," said Kelley. "There is nothing more we can do for the [Pacific] Northwest. They have to get their habitat under control. In Alaska, we've given and haven't seen the benefits."