Outgoing U.S. Ambassador Deane R. Hinton, in one of his last public appearances here, today attacked what he called "the relative silence" of this country's private business leaders in the face of continued and increasing murders of suspected leftists and guerrillas.

In a speech to the Salvadoran American Chamber of Commerce and particularly in response to questions afterward, Hinton expressed some optimism about the general course of events during his two years as ambassador, but he was sharply critical of problems in the government and Army that he said he may not live to see resolved.

Hinton, 60, recited what an aide described as "a laundry list of what the country needs to change," a litany of what he "hopes for" that one embassy staffer noted "has a lot of barbs in it."

He said the greatest setback of his tour here was the inability to get convictions in El Salvador's courts of soldiers who allegedly murdered American nuns in one attack and U.S. labor advisers in another.

"Personally, I have been most frustrated by the failure to date to see justice done to the killers of my fellow citizens," Hinton said. "I think all Americans share a sense of outrage over this failure."

But Hinton's criticisms extended even to the U.S. Congress as he surveyed the conflict here in his prepared remarks.

Both Salvadoran President Alvaro Magana and President Reagan, he said, "confront grave internal divisions. Political leaders within Congress and within the Salvadoran constituent assembly, to say nothing of others in our pluralistic society, often see matters differently than the two presidents, putting their personal and party interests first."

Hinton's replacement was announced in May amid statements by senior Reagan administration officials suggesting that the senior career diplomat was "burned out."

Today in his speech he carefully balanced his criticisms of the government here with attacks on the "communists" fighting to overthrow it.

He said he had no significant differences with Reagan administration policy and suggested that what Washington wants for El Salvador is what the Salvadoran people want for themselves: democracy, prosperity and peace free from dictatorships of the extreme left or right.

But in response to questions from an audience that included members of the conservative "oligarchy" that long dominated El Salvador's social and political as well as economic life, Hinton returned to themes stated in a controversial speech before this same group last October.

Although he did not use today, as he did then, the terms "mafia" and "gorillas" to describe ruthless and wealthy right-wing forces here that appear immune to arrest or punishment, Hinton clearly was addressing that group.

Hinton's sharpest remarks came when he responded to a question from the audience asking him to provide data that would indicate that right-wing terrorism here is in any way comparable to that of the left.

"Killing people outside the legal process is unacceptable for a civilized people if it comes from you, from me, from the right, from the left," Hinton said. "It is not a quantitative question, it is a qualitative question.

"When there are people found here in the parking lot of the Camino Real Hotel strangled, with plaques saying 'We've killed them because we are the Secret Anticommunist Army,' " Hinton said in reference to an incident here, "that is not acceptable and ought not to be acceptable for you, and frankly I ask myself why there are people here who ask questions like that."

Hinton added, "I have never understood the relative silence of the active forces in the private sector" on death squad killings.

"Several of you have explained to me in private that you share my point of view but that it would be dangerous for you personally to say it" publicly, Hinton said. "I understand. There is too much fear. Someone has to change; someone has to run the risk."

As he has before, Hinton called today for patience from the U.S. people in dealing with El Salvador's complex problems. But he noted difficulties "arising from the legacy of 50 years of repressive, autocratic government, arising from the debilitating tradition of armed forces above the law in practice, although not in theory or constitutionally."