President Carter, in a farewell address to the nation from the White House, urged Americans last night to cling to the country's "time-honored principles and commitments," including three of the distinctive themes of his presidency -- human rights, nuclear disarmament, and conservation of the environment.

At the end of the 17-minute speech from the Oval Office, the president departed from his text to mention the hostages in Iran, the problem that plagued the last year of his presidency. He pledged, in the 5 1/2 days left to him in power, to continue to "work hard and pray for the lives and the well being of the American hostages.

"I can't predict what will happen, but I hope you will join me in my constant prayer for their freedom," he said.

But otherwise, Carter, who spoke from a chair in front of his desk, did not speak of the specific issues he grappled with and his successor will inherit next week. Instead, he sought to focus attention one final time on the three broad areas he spoke of so often during his tenure as the nation's 39th chief executive.

He also warned that the office of president, which he said, without criticism, is "among the most severely constrained by law and custom" in the world, must not be weakened, and he took one final swipe at the "single issue groups and special interest organizations" with whom he fought, often unsuccessfully.

The growing power of such groups, the departing president said, "is a disturbing factor in American political life. It tends to distort our purposes because the national interest is not always the sum of all our single and special interests. We are all Americans together -- and we must not forget that the common good is our common interest and our individual responsibility."

But Carter made no suggestions on how to preserve and strengthen the powers of the presidency. Of his successor, Ronald Reagan, who arrived in Washington last night to await inauguration, Carter said: "I understand, as few others can, how formidable is the task the president-elect is about to undertake. To the very limits of conscience and conviction, I pledge to support him in that task. I wish him success, and Godspeed."

White House press secretary Jody Powell said Carter deliberately decided not to speak of specific "prescriptions and programs" for fear he would give the impression he was "initiating debate with the incoming administration."

As a result, Carter's remarks were general and his central message an appeal to Americans not to ignore the great dangers of the modern world, such as nuclear war, or to abandon the nation's traditional ideals as the United States moves through "a time of transition, an uneasy era which is likely to endure for the rest of this century."

"During this period," he said, "we may be tempted to abandon some of the time-honored principles and commitments which have been proven during the difficult times of past generations.

"We must never yield to this temptation," he continued. "Our American values are not luxuries but necessities -- not the salt in our bread, but the bread itself. Our common vision of a free and just society is our greatest source of cohesion at home and strength abroad -- greater even than the bounty of our material blessings."

The president repeated the Declaration of Independence's commitment to "life, liberty and the pursuit of happiness" and added:

"Each generation must rediscover the meaning of this hallowed vision in the light of modern challenges. For this generation, life is nuclear survival; liberty is human rights; the pursuit of happiness is a planet whose resources are devoted to the physical and spiritual nourishment of its inhabitants."

The issues Carter chose to speak of last night were not surprising, for they formed some of the main themes of his presidency. They are also issues over which he and Reagan often differed sharply during the election campaign, and while the president pledged to support his successor he also indirectly reiterated his side of the arguments and suggested the great issues on which he thinks the Reagan administration should be measured.

Warning that "it may only be a matter of time before madness, desperation, greed, or miscalculation lets loose this terrible force" of nuclear weaponry, the president said the United States must remain militarily strong but with other countries must also "find ways to control and reduce the horrifying danger that is posed by the world's stockpiles of nuclear arms."

Speaking of the environment, he warned that "there are real and growing dangers to our simple and most precious possessions: the air we breathe, the water we drink, and the land which sustains us."

"If we do not act, the world of the year 2000 will be much less able to sustain life than it is now," Carter said.

As for human rights, the main theme of his foreign policy, the president asked Americans to support "the strengthening of democracy, and the fight against deprivation, torture, terrorism and the persecution of people throughout the world."

The world, Carter said, yearns for freedom, human dignity and justice. "I believe with all my heart that America must always stand for these basic human rights -- at home and abroad," he declared. "That is both our history and our destiny."