The Senate Foreign Relations Committee heard a barrage of conflicting opions yesterday about Ernest W. Lefever, President Reagan's controversial nominee to head to U.S. human rights program. But perhaps the most gripping testimony at his confirmation hearing came from a witness who did not address the committee.

He was Jacobo Timerman, an yargentine newspaper editor who inquired into the disappearance of thousands of Argentinians in the 1970s and who subsequently was jailed for 20 months before being allowed to emigrate to Israel. His book about his ordeal, "Prisoner Without A Name, Cell Without a Number," is now being published in this country.

During the committee's two days of hearings on Lefever, Timerman's case has been cited repeatedly by liberal members and by witnesses hostile to Lefever's position on human rights. Lefever advocates abandoning the tough human rights stance taken by the Carter administration toward rightist dictatorships in favor of a "quiet diplomacy" apporach based on friendlier relations and persuasion.

Timerman briefly visited the hearing yesterday as a spectator, and when Chairman Charles H. Percy (R-Ill.) asked him to stand, the overflow crowd burst into thunderous applause. Later, Timerman, while stressing that hw was not commenting on Lefever's nomination, made it pointedly clear that he regard the Reagan administration's policy as an abandonment of the human rights cause.

Talking with reporters, he said the turning point in his struggle to win freedom was a visit to Buenos Aires by Patt Derian, the outspoken assistant secretary of state for human rights in the Carter administration and the principal exponent of the policies that Reagan and Secretary of State Alexander M. Haig Jr. want to jettison. Timerman Said:

"On the day she came, that made a great difference. I know positively how many lives were saved because Patt Derian was making a great scandal. She was always outspoken. There is no other way."

He added: "A silent diplomacy is silence; a quiet diplomacy is surrender."

His words dramatically underscored one side of the argument before the committee, which yesterday heard a small army of witnesses -- split almost evenly along liberal-conservative lines -- debate whether Lefever and his ideas are an appropriate replacement for Derian's activism.

The day-long hearing gradually came to seem like a monotonous tennis match with the participants -- members of Congress, academicians, representatives of various rights groups -- lobbing praise and criticism for Lefever back and forth.

His foes trained their fire on Lefever's contention that the United State should take a tougher line on rights violations by totalitarian regimes such as the Soviet Union than toward those committed by authoritarian regimes whose foreign policies are friendly to this country. As Rep. Tom Harkin (D-Iowa) said, the United States will "risk losing the affection of other peoples, as we did in Iran," if it fails to condemn abuses everywhere.

On the other side, Lefever's supporters praised him as possessing a genuine concern for human rights, and, as Sen. John Tower (R-Tex.) said, advocating an approach that is more realistic, more balanced . . . not a dual standard which had berated the human rights shortcomings of our friends and ignored the brutal oppression of our enemies."

As Monday's severe grilling of Lefever by the committee's Democrats and some of its majority Republicans indicated, the vote on his nomination is going to be close and could result in the committee failing to give him its approval. But even if it dies, he still could be confirmed by the full, Republican-controlled Senate, where conservative feeling and loyalty to Reagan are stronger.

Committee sources said the vote could come today, but they added that such factors as members' desires to review the full hearing record and the need to examine financial records of a public policy center headed by Lefever probably will delay a vote until after the congressional recess next week.

The White House yesterday reaffirmed Reagan's support for Lefever. Deputy press secretary Larry Speakes, asked about the pummeling Lefever took when he testified Monday, said: "He's our nominee, and we chose him beause we think he's the man for the job."