It is "entirely possible" that the United States will take direct action against Cuba if arms shipments to guerrillas in Salvador do not stop, Edwin Meese III, counselor to President Reagan, said yesterday.

Meese's warning was the latest in an escalating series of U.S. statements on the flow of arms to the leftist forces in El Salvador's civil war. The Reagan adminstration claims to have incontrovertible evidence that the arms are being shipped from Cuba.

"I think it's entirely possible if the arms shipments don't cease," Meese replied when asked if the United States would act to punish Cuba directly for its asserted role in supplying the guerrillas,

He refused to rule out a blockade of Cuba. "One of the things you don't do is rule out anything," Meese said. He referred to Reagan's stated desire to have America's foes go to bed each night uncertain what Washington's next move might be.

Meese said he hopes Havana's leaders realize it is in Cuba's self-interest to stop the arms shipments "right now."

President Reagan told reporters today before returning to Washington from his ranch in Santa Barbara, Calif., that he is "very concerned" about political instability in El Salvador and by communist military aid to the Central American nation.

The president confirmed recent remarks by Secretary of State Alexander M. Haig Jr., who said the United States has established continegency plans to stem the flow of weapons from communist sources into El Salvador.

Asked if he conceives of a situation that would call for U.S. military involvement in El Salavdor , Reagan said, "Here again, I just don't think it's right to comment. . . ."

The administration's options are not limited to use of military force, Meese said on ABC's "Issues and Answers." They include economic reprisals and intensified efforts to inform the leaders and peopele of other nations about the El Salvador crisis.

A substantial part of the arms reaching the Savladoran guerrillas comes through Cuba, according to U.S. officials.

The Reagan administration has also been putting heavy pressure on another reported intermediary, Nicaragua, to halt the flow of arms into El Salvador. The United States threatened to end all aid to Nicaragua, a country with severe economic problems, and reportedly received a private pledge that Nicaragua's leftist government would move to stop the traffic through its territory.

The Reagan administration has made the arms shipments to the first test of its new hard line toward the Soviet Union and its ally, Cuba.

Meese said the United States is determined to show Moscow that the Soviets "cannot act with impunity" and "to prevent the expansion of communism."

Meese said the cold war never ended and that the Soviet Union has always continued its cold war confrontational policies.

The Soviet leadership must learn it cannot have normal trade relations with the United States at the same time that it is pursuing a policy of military expansion, Meese said.

Elsewhere, U.N. Ambassador Jeane Kirkpatrick attacked the Carter administration's human rights policy yesterday as utopian and arbitrary, and said it helped weaken the United States so that it now faces a ring of Soviet bases around its borders.

The Reagan administration will not abandon human rights but will change its approach, taking into account "the concrete circumstances in which a human rights violation takes place" and recognizing that "there are degrees of evil," Kirkpatrick said in an interview with U.S. News & World Report.

But Patricia Derian, former assistant secretary of state for human rights, defended the Carter Policy in a parallel interview. She said it was successful and "in our long-range national interest."

"Countless numbers of people are alive today because of our policy," she said. "Torture has been reduced somewhat. A number of countries have returned to civilian government. Thousands and thousands of people who were in prison are now free."

Kirkpatrick said the Reagan administration will not expect reforms to be carried out in a country like El Salvador, which is fighting a civil war, but will trust the judgment of Napoleon Duarte, the military junta leader "known as a social reformer."

"Our position in the Western Hemisphere has deteriorated to the point where we must now defend ourselves agains the threat of a ring of Soviet bases being established on and around our borders," Kirkpatrick said.

Carter's human rights policy "certainly played a role" in bringing about this situation, she said.