President Reagan called last night for "a second American revolution of hope and opportunity" in a State of the Union address that celebrated economic and scientific achievements and made scant mention of the spending sacrifices his new budget asks of a broad spectrum of Americans.

"Let us begin by challenging conventional wisdom: there are no constraints on the human mind, no walls around the human spirit, no barriers to our progress except those we ourselves erect," Reagan said in the nationally televised speech to a joint session of Congress on his 74th birthday.

Reagan, who was greeted with a long standing ovation when he entered the House chamber and frequently was interrupted by applause, concluded his speech by introducing two "heroes" he said epitomized American values: Jean Nguyen, who fled Vietnam with her family after the fall of Saigon and is to graduate from West Point in May, and Clara Hale, a woman from Harlem who cares for the children of heroin addicts.

While hailing the "new freedom" he said his administration had brought to America, the president added, "We are not here to congratulate ourselves on what we have done, but to challenge ourselves to finish what has not yet been done."

His list of unfinished domestic business ranged from passage of tax simplification to construction of a manned space station. He also spoke of further business deregulation, initiatives to provide "full and equal power" for minorities and preservation of what he called "the social safety net for the elderly, needy, disabled and unemployed."

Reagan's speech avoided partisan criticism of Congress and was noticeably less combative in many of his references to the Soviet Union than many speeches of his first term. But he denounced the leftist Sandinista government in Nicaragua and pledged his continued support for "freedom fighters" there and in Afghanistan.

In foreign policy, Reagan called for "the united support of the American people" in upcoming arms control negotiations with the Soviet Union. He repeated his call for increased military spending, saying that "our determination to maintain a strong defense has influenced the Soviet Union to return to the bargaining table."

Reagan made specific pleas for two favorite military projects, the MX intercontinental ballistic missile, which he calls "the Peacekeeper," and the controversial Strategic Defense Initiative or "Star Wars" plan aimed at developing a non-nuclear defense against nuclear missiles.

The most passionate language of the speech was devoted to the Strategic Defense Initiative, which Reagan called "the most hopeful possibility of the nuclear age," adding, "but it is not very well understood."

"Some say it will bring war to the heavens but its purpose is to deter war, in the heavens and on Earth," Reagan said. "Some say the research would be expensive. Perhaps, but it could save millions of lives -- indeed, humanity itself."

Reagan said the Soviets are well ahead in strategic defense and responded to those who say U.S. research into an effective system would take a long time by saying, "Let's get started."

Though Reagan did not specifically request financial support for another controversial aid proposal, covert financial aid for U.S.-backed rebels opposing the Sandinista government, administration officials said Reagan again intends to seek more funds for this purpose from a reluctant Congress. The president referred to this in saying "it is essential that Congress continue all facets of our assistance to Central America."

Reagan reserved his harshest language for the Nicaraguan regime.

"The Sandinista dictatorship of Nicaragua, with full Cuban Soviet-bloc support, not only persecutes its people, the church and denies a free press, but arms and provides bases for communist terrorists attacking neighboring states," Reagan said.

A spokesman for the Nicaraguan Embassy said that Reagan's address presented "an image of Nicaragua that does not correspond to reality" and that the only terrorism there is "the criminal action of the 'contra' forces who every day murder innocent civilians."

The reference to Cuban support for Nicaragua was the president's only mention of Cuba, which he has often pointedly criticized in the past. Administration officials who briefed reporters on the speech said better relations with Cuba would be welcomed but were restrained in predicting whether this might occur.

Reagan also appealed for economic aid to help underdeveloped nations. He said that many of the 3 billion people in Third World countries "are victims of dictatorships that impoverish them with taxation and corruption" and asked U.S. allies to join in "a practical program of trade and assistance that fosters economic development through personal incentives."

"We cannot play innocents abroad in a world that is not innocent," Reagan said. "Nor can we be passive when freedom is under siege. Without resources, diplomacy cannot succeed; our security assistance programs help friendly governments defend themselves, and give them confidence to work for peace."

Reagan began his address by contending that, "after four years of united effort, the American people have brought forth a nation renewed -- stronger, freer and more secure than ever before.

"Four years ago, we said we would invigorate our economy by giving people greater freedom and incentives to take risks, and letting them keep more of what they earned," Reagan said. "We did what we promised, and a great industrial giant is reborn."

The president then ticked off a series of statistics demonstrating economic growth and went on to say that "new freedom in our lives has planted the rich seeds for future success."

Defending the income tax reductions he sponsored during his first term, Reagan said they had "freed our economy to vault forward to record growth." He did not link these tax cuts to the soaring federal deficit, as many critics do, and instead repeated a familiar declaration of his 1984 presidential campaign that "the best way to reduce deficits is through economic growth."

"More businesses will be started, more investments made, more jobs created and more people will be on payrolls paying taxes," Reagan said. "The best way to reduce government spending is to reduce the need for spending by increasing prosperity."

Many of the proposals Reagan made last night were familiar features of earlier speeches. But he gave more emphasis than in the past to themes of social justice and to economic help for minorities.

The proposals include enterprise zones that would provide tax incentives in depressed urban areas, a lower minimum wage for teen-agers, support of the Job Training Partnership Act, tuition tax credits and health vouchers and encouragement for low-income public housing residents to own and manage their dwellings.

When Reagan talked about enterprise zones he ad-libbed a comment to House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who sat behind him throughout the speech.

"Now, Mr. Speaker, I know we agree that there must be no forgotten Americans," Reagan said. "Let us place new dreams in a million hearts and create a new generation of entrepreneurs by passing enterprise zones this year. And, Tip, you could make that a birthday present."

On social issues, he called again for constitutional amendments to permit school prayer and ban abortions.

"Abortion is either the taking of human life or it isn't," he said. "And if it is -- and medical technology is increasingly showing that it is -- it must be stopped"

He also called for limiting the rights of defendants in criminal cases, asking rhetorically, "Shouldn't we feel more compassion for victims of crime than for those who commit crime?"

Reagan said that, despite increases in the convictions of drug dealers and organized crime leaders, America must do more to stop criminals. His list included continued use of the death penalty and passage of legislation that would allow the use of evidence obtained illegally when it was done in good faith by police officers.

The only passages of the speech dealing with sacrifice to reduce the deficit called for reduction or elimination of "costly government subsidies." Reagan cited Amtrak and farm subsidies and asked Congress for a trial use of the line-item veto, which he employed as governor of California.

"I hope you will pass and send that legislation to my desk," Reagan said. "Nearly 50 years of government living beyond its means has brought us to a time of reckoning."

The budget cuts Reagan seeks in the nation's major health care programs, Medicare and Medicaid, were confined to a single sentence in which the president said health spending "will be slowed, but protections for the elderly and needy will be preserved."