Former president Jimmy Carter yesterday accused the Reagan administration of abdicating its responsibility as a world leader in environmental protection by undercutting international efforts and attempting to thwart the Environmental Protection Agency's enforcement of the law.

In his harshest criticism of his successor to date, Carter also accused President Reagan of ignoring poverty and oppression in El Salvador in pursuit of military aid for "the most murderous government in this hemisphere."

"It is tragic indeed for our leaders to ignore these clear warning signals and to allege that they are just the result of ill-advised foreign political decisions or a communist plot against us," Carter said in an address to the Global Tomorrow Coalition, an alliance of 64 environmental, conservation and population-control groups established to work for the recommendations in the Global 2000 report.

That report, a three-year study commissioned by Carter and released during the last year of his term, warned that without concerted international action the world faced a future of hunger, environmental degradation and political tensions.

Since its release, Carter said, several other nations have adopted the report as a basis for shaping their national policies.

"Our own government's actions, unfortunately, have been characterized by opposition to the recommendations--by retrogression and not progress," he said. "The needs we identified before January 1981 are now much more acute."

In his address and in a news conference later, Carter cited the administration's "obstruction" of an international Law of the Sea Treaty and its deep cuts in international research funding as examples of "inaction" that "exacerbates existing human suffering."

"The deliberate, across-the-board abandonment of U.S. leadership on environmental, resource and related global issues is of grave concern to us all," he said. "During the past 2 1/2 years we have stood almost alone among nations in our refusal to cooperate with international efforts."

In his news conference, Carter said that under pressure from his administration El Salvador was just beginning to correct human rights violations and initiate land reforms and free elections.

"For a time, we were making progress . . . ," he said. "But those restraints have been abandoned and now it is just a tough militaristic confrontation that is being engendered there, ignoring the basic needs and suffering of the people."

Carter also criticized Reagan's defense policies, calling his so-called "Star Wars" proposal for a laser anti-ballistic missile system "ill-advised" and contrary to previous agreements with the Soviet Union.

Alan Hill, chairman of the White House Council on Environmental Quality, defended the administration's record against the assaults by Carter and other speakers at the conference's opening session, warning that trends and forecasts are not "an infallible crystal ball."

But Carter, who has agreed to contact foreign leaders on behalf of the coalition, urged private and political leaders to take action on their own to deal with the problems identified in the Global 2000 report.

The report has been attacked by a counter-report that called its conclusions "dead wrong" and said the world will be richer, less polluted and more peaceful in the year 2000 if current trends continue.

Max Singer, a Washington consultant who worked on the second report, commissioned by the Heritage Foundation and released last week, told the conference yesterday that the Global 2000 report was "founded on a fundamental error" and is an "attack on the moral foundation of the United States."

"Our triumph is mass production and mass consumption, as well as democracy," he said. "Since this report undermines our moral position, why use it?"

Both Carter and Russell Peterson, president of the National Audubon Society and chairman of the Global Tomorrow Coalition, dismissed Singer's arguments and the conclusions of the second report. "It is a call to inaction," Peterson said. "Ours is a call to action."

Carter later told reporters he did not expect the issues of environmental protection or nuclear arms control to become 1984 campaign issues until after the primaries.

He also said that he did not expect to be a part of the primary campaign, and would be involved in the general election only if the Democratic nominee wanted him.

"I'm not presuming that a Democratic candidate will want me or anyone else wrapped around his or her neck," he said.

But an earlier comment suggested that Carter is not counting on a Democratic administration come 1985. Asked about the impact of the Reagan administration's environmental policies, he responded: "We can live with it four, possibly eight years--I dread the thought--and still be a great country."