Foes of the new Panama Canal treaties opened fire on the pacts yesterday, with their most prominent spokesman, Ronald Reagan, charging the Carter administration with ignoring human-rights violations by "the repressive regime in Panama."

The former California governor spoke out as opponents and supporters of the agreements turned their attention from the ceremony of Wednesday's formal treaty signing to the next phase of the continuing canal controversy.

That involves the impending fight to win the Senate approval necessary to put into effect the treaties giving Panama control over the canal by the end of the century.

On the morning after President Carter and Panama's military ruler, Gen. Omar Torrijos, signed the treaties, both sides had representatives on Capitol Hill seeking to marshal congressional support for their respective positions.

While Reagan led a parade of hostile witness testifying before a Senate Judiciary subcomittee, the two treaty negotiators, Ellsworth Bunker and Sol M. Linowitz, were on the other side of the Capitol, arguing the merits of the treaties before the House International Relations Committee.

Bunker and Linowitz received a lopsided favorable reaction from most members of the House committee. However, Reagan had a uniformaly supportive audience in the Senate hearing, attended only by senators outspokenly critical of the treaties.

At stake is whether the opposition can prevent the administration from mustering the 67 votes needed in the Senate for approval. Unofficial counts taken this week by the NBC and ABC television networks indicated that an answer to this question won't be forthcoming for some time.

The NBC poll showed 35 senators in favor or leaning toward approval, 22 opposed for leaning toward a negative vote and 43 undecided. ABC counted 33 for or leaning toward support, 27 against or leaning toward opposition and 40 undecided.

Most of the attention yesterday centered on Reagan, the hero of Republican conservatives and the man many treaty opponents hope will become the symbolic leader of their cause.

Reagan's testimony before the Subcommittee on Separtion of Powers attacked the treaties on a broad range of constitutional, strategic and foreign policy points. In many respects though, the most revealing part of his testimony involved his attempt to bring human-rights considerations into the treaty debate.

That followed what strategists for the anti-treaty forces say privately will be an increasingly heard theme in their attacks - an attempt to turn Carter's much-publicized championing of human rights against the administration.

Charging that the United States cannot afford "a double standard in this most fundamental of areas," Reagan said:

"Human rights criticism has been leveled at a number of nations in the Western Hemisphere which have always been friendly toward up, yet I cannot recall a single word of criticism by any representative of our government toward Panama in this regard."

Noting that the Torrijos government is a military dictatorship, Reagan cited a study by Freedom House, a private organization that attempts to monitor repressive practices throughout the world. Freedom House, he said, "rates Panama as one of 67 nations in the world that is 'not free.'"

An echo of this theme was heard on the other side of the Hill, where House members questioned Bunker and Linowitz closely about the human rights issue.

Bunker replied that Panama's record, "while not perfect, cannot be said to be horrible." He noted that, in 1975, Amnesty International did not include Panama on its list of countries engaging in torture, and he also cited a recent State Department report saying that, while the Torrijos government has exiled opponents, it currently does not appear to be involved in incidents of brutality for political purposes.

Another issue debated at length yesterday involved that contention of treaty opponents that the Constitution gives to the Congress sole power to dispose of territory and federal property and that Carter therefore lacked authority to negotiate the treaties without enabling legislation from Congress.

In support of this argument, Reagan cited several past instances when the transfer of property or land in the Canal Zone was preceded by the incumbent administration going to Congress and asking for such authorization.

However, at the House hearing, State Department legal adviser Herbert J. Hansell, noting the President's constitutional authority to negotiate and enter into treaties, said State and the Justice Department both have concluded that there is "concurrent authority" to transfer territory either by treaty or by Senate-House action.

Linowitz and Bunker also told the committee that, in addition to greatly increased revenues from canal tolls, the United States plans to give up to $295 million in economic aid and credits and to ask Congress to provide Panama with $50 million a year over 10 years in military sales credits.

Asked what the United States would receive in return for this financial outlay, Linowitz replied: "The most important thing we get is the enchanced assurance of a continued, open, accessible, secure, neutraal canal." CAPTION:

Picture 1, Ronald Reagan testifies before Senate Judiciary subcommittee, while negotiators Ellsworth Bunker and Sol M. Linowitz appear before House Panel. By James K. W. Atherton - The Washington Post; Picture 2, Sen. John Sparkman (D-Ala.), chairman of the Senate Foreign Relations Committee, greets Gen, Omar Torrijos, military ruler of Panama as he arrives for a luncheon for Latin American leaders at the Capitol yesterday. UPI