Six weeks of the Iran-contra hearings have given the world a disturbing portrait of Ronald Reagan's presidency. In the apt description of Sen. William S. Cohen (R-Maine), the testimony has provided "a tale of two governments -- one elected, the other procured."

Both governments, however, were the responsibility of the president, which is why these hearings already have had such a profound impact on Reagan's presidency.

What has unfolded from the 18 witnesses who have appeared so far is a story of contempt: for Congress, for public, for legalities, for the normal processes of government and diplomacy. The Iran-contra testimony reveals a classic example of an end-justifies-the-means mentality at work secretly in the White House.

In this, the Iran-contra hearings both resemble and markedly differ from the Watergate inquiry 14 years ago that ended Richard M. Nixon's presidency.

As with Watergate, the attitudes that led to these hearings have entrapped the president and his administration in a situation from which there seems no escape.

The latest example of the pervasive effect of the hearings was Reagan's news conference in Venice last Thursday concluding the economic summit of western allies.

Usually such an occasion, in such a setting, offers a president an opportunity to demonstrate his world leadership role. Instead, it showed Reagan's inability to extricate himself from Iran-contra hearing disclosures. He was peppered from beginning to end with questions stemming directly from the more than 100 hours of congressional testimony to date.

A striking difference exists, though, between Iran-contra hearing witnesses and those of the Watergate scandal.

In the Watergate hearings, many witnesses testified to a feeling of contrition for violating public trust and circumventing, or breaking, the law. Most notable was White House aide Jeb Stuart Magruder, who publicly apologized to the country and to his family for the actions that led him to the witness stand and, ultimately, to jail.

With one exception -- the tormented, half-apologetic, half-defensive testimony of Reagan's former national security adviser, Robert C. McFarlane -- Iran-contra witnesses have been strikingly unrepentant. Their testimony has been characterized by a near-uniform degree of certainty about the rightness of their actions regardless of legalities -- an attitude best exemplified by the remark of Lt. Col. Oliver L. North's former secretary, Fawn Hall, that there are "times when you have to go above the written law."

In the first phase of the hearings, the House and Senate select committees focused on the way in which American officials and their private operatives enabled arms and cash to flow secretly to Nicaraguan contras despite a congressional ban on such aid by the government. This concentrated approach resulted in the single most important disclosure to emerge from the hearings so far: a serious breakdown in the system of political checks-and-balances between executive and legislative branches.

Short of evidence that could lead to an impeachment proceeding -- which the committee members interviewed for this article uniformly said they do not expect -- the most likely effect of the hearings involves the redressing of that balance in favor of Congress at the expense of the president.

Strong and unrefuted evidence of extended, deliberate efforts to mislead and deceive Congress about the reality of administration actions in Central America has produced virtual unanimity of opinion on the committees that a grave betrayal of trust occurred. Lawmakers of both parties express determination to check what they regard as abuses of power in the future.

This is true even among those on the committees who have argued that the congressional ban on aid to the contras, as expressed in several versions of the now-famous Boland Amendment, does not apply to the president or the National Security Council and will not stand legal review from the courts. The hearings have documented beyond argument that officials involved believed they were operating illegally -- which is why they went to such extraordinary lengths of secrecy, employing code names, cash, Swiss bank accounts, planes and ships that supposedly could not be traced back to U.S. agencies, whether the Central Intelligence Agency, Defense Department, National Security Agency or the NSC, which had daily clandestine operational authority.

In that respect, the testimony of Assistant Secretary of State Elliott Abrams was critical and symbolic.

Abrams, the highest official to appear so far and the person charged with carrying out the president's Central American policy, acknowledged that he had repeatedly misled Congress about the extent of U.S. involvement in the secret efforts to supply the contras.

His testimony infuriated many committee members of both parties. It led to a broad, bipartisan consensus that Abrams must be removed from his position. Despite the strong public backing Abrams subsequently received from Secretary of State George P. Shultz, the president's tepid endorsement of Abrams in response to press questions in Venice makes it unlikely he will survive. Congress has made it clear that if Abrams stays, the president's contra aid policy, already seriously imperiled, will be in danger of extinction.

Other consequences of the hearings' impact on the president's conduct of foreign policy are apparent. Strengthened congressional resolve in insisting on greater and far more candid consultation over critical issues has forced the White House to hesitate over planned U.S. naval escort missions for Kuwait in the Persian Gulf. It also forced the administration to withdraw its plan to sell 1,600 antitank missiles to Saudi Arabia.

Nor are the effects of this new congressional reassertion of power limited to foreign policy. The administration faces increasingly rigorous examination of all its proposals and policies in the aftermath of Iran-contra revelations of administration double-dealing.

The hearings have resulted in two other significant disclosures.

Before they began, the administration attempted to leave the impression that any wrongs committed were limited to a few people -- or even to one, North, who was fired from the NSC staff -- operating beyond White House control and acting without higher authority.

Iran-contra testimony has demolished that contention.

Witnesses, whether present or former officials or private entrepreneurs, have repeatedly testified that they believed they were acting under the president's official sanction while North has been shown to have been deeply involved with other high officials, notably the late CIA director, William J. Casey.

The president's name has been invoked almost daily during the hearings. In the process, and following testimony by former national security adviser McFarlane that he had briefed Reagan "dozens of times" on secret Iran-contra activities, the White House dropped its earlier claim that the president didn't know much about what was happening. Reagan acknowledged that he was fully informed and it had been his idea from the beginning to get aid to the contras.

This position shifted again last week. In Venice, Reagan was asked about those who testified that they believed they had acted, as a reporter put it, "with your blessing and under the full authority of you."

Reagan's answer was that "maybe some people were giving the impression that they were acting on orders from me . . . {but} I wasn't giving those orders because no one had asked or had told me what was truly happening there."

A second disclosure, documented by congressional evidence and testimony, involves the extent of official involvement in what has been shown to have been an attempt at a cover-up.

Hall's testimony about shredding, altering and removing critical NSC documents was the most dramatic on the extent of the cover-up attempts, and there is much more to come in this line of inquiry.

What remains almost unexamined after six weeks are two greater questions: Why did these events occur in Reagan's second term and who authorized them?

So far, the committees have not explored the psychological and ideological atmosphere inside the White House and the executive agencies serving the president that produced the climate in which the secret Iran-contra activities flourished.

The expectation among key committee members is that the second phase of the hearings, set to start June 22 and focusing more on presidential decision-making over U.S.-Iranian arms-for-hostages deals than aid to the contras, will be more illuminating and produce more damaging disclosures.

For the White House, already preoccupied by the Iran-contra affair, the likelihood thus is that the next month of hearings will pose even more difficult problems.