President Reagan last night began the selling of his second term with a reach for the political high ground. He brushed past criticism of his new budget and its long line of deficits in favor of an upbeat appeal to the nation to complete the conservative revolution in government he began four years ago.

The president took the offensive in glittering rhetoric in his State of the Union address, leaving little doubt that he intends to use his personal popularity and the mandate he received in winning 49 states last November to keep the pressure on his opponents.

If there is disagreement over the specifics of what Reagan has laid out -- and the lukewarm applause over many of the president's programmatic prescriptions suggested there is -- there appeared to be little debate over who is in control.

From the warm ovation that greeted the president's entry in the House chamber to the chorus of "Happy Birthday," marking what Reagan called the 35th anniversary of his 39th birthday, the joint session of Congress paid tribute to the president's political prowess.

And when Reagan honored two "American heros" -- Jean Nguyen, a Vietnamese refugee now at West Point, and Mother Clara Hale, who works with the children of drug addicts in Harlem -- one prominent Democrat shook his head in obvious admiration for the president's mastery of the moment.

The opposition Reagan faces over his budget cuts was quickly apparent from the statement issued by House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) moments after the president left the chamber.

"Tonight President Reagan spoke beautifully of his program and of the future he believes it promises," O'Neill said. "I hope the president will be as persuasive and as eloquent in spelling out the details of his program . . . . Tonight was a night of eloquent generalities. Tomorrow he must begin to inform people of the sometimes difficult realities of the Reagan revolution."

In the Senate, Majority Leader Robert J. Dole (R-Kan.) and Budget Committee Chairman Pete V. Domenici (R-N.M.) praised the speech but expressed regret that Reagan did not put more emphasis on deficit reduction.

"I would have stressed it a bit more, but you can't talk about everything every time, I guess," Dole said.

Since his reelection, Reagan has been under fire from Democrats and some members of his own party for not moving forcefully to reduce the deficits and for backing significantly higher defense spending.

But with Senate Republicans bogged down in their own effort to write a budget, which Dole had predicted would be completed before the president's package arrived on Capitol Hill, Reagan once again has assumed center stage in the debate.

Last night, Reagan leapfrogged his critics, sounding neither confrontational nor yielding. He did it with glowing phrases aimed at inspiring the public rather than persuading the Congress. He spoke of America's "invincible spirit," of "a great industrial giant" reborn, of his "great plans and great dreams." In calling for an end to abortion, he said "we can fill the cradles of those who want a child to love."

In plain English, he urged action on his Strategic Defense Initiative, or "Star Wars," proposal. "Some say the research will take a long time," he said. "The answer to that is, 'Let's get started.' "

Denunciation of the Democrats, whom Reagan has blamed in the past for America's economic ills, was largely missing, a reflection in part of the Republican belief that the opposition party is in disarray.

Instead, Reagan issued a strong call for bipartisan tax simplification and coolly defended his budget priorities of no new taxes, the elimination of many middle-class subsidies, and more money for the Pentagon. "You know, we only have a military industrial complex until a time of danger," he said. "Then it becomes the arsenal of democracy."

He also argued that his arms buildup "influenced the Soviet Union to return to the bargaining table."

Another old Reagan nemesis was mostly missing last night. The budget deficits that four years ago threatened the republic seemed barely visible on the economic horizon in Reagan's portrait of an America "poised for greatness."

Rhetorically at least, Reagan made his most direct appeal to blacks and other minorities. His prescriptions included a list of leftover initiatives from his first term, including urban enterprise zones and a lower minimum wage for young workers.

But if the proposals were old, their prominence in Reagan's speech reflected the administration's desire to chip away at the image of Reagan as a president who has hurt blacks and the poor, and in the process woo some middle-class blacks away from the Democratic Party.

In tone and substance, Reagan appeared last night to side with the so-called young turks of his own party, challenging Republicans to create a society of "opportunity" and "freedom." It was a speech many younger Republicans had hoped Reagan would deliver last August at the Republican National Convention in Dallas.

"It was music to my ears," said Rep. Jack Kemp (R-N.Y.), a cosponsor of tax simplification and a leader of younger Republicans in the House.

But Sen. Mark O. Hatfield (Ore.), a liberal Republican, was sharply critical, saying the president was "about to shatter accepted notions of the impossible by attempting to save the earth by militarizing space, eliminate nuclear weapons while producing them with abandon and assuming we will reduce the deficit in the process."

In speeches to joint sessions in 1981 and 1982, Reagan dwelt at length on the programmatic details of his economic plan. Last night, he largely submerged his governmental wish-list, which again included a constitutional amendment to balance the budget, school prayer and legislation to prohibit abortions.

Instead, he extolled the virtues of old-fashioned American values, emphasizing them as much as his tax and spending priorities.

"Of all the changes that have swept America the past four years, none brings greater promise than our rediscovery of the values of faith, freedom, family, work and neighborhood," he said.