President Reagan emerged from the most extended rough patch of his presidency last week with his biggest victory.

In a striking turnabout, Reagan came off a fumbling press conference performance, several flat speeches and a stretch of light workdays to demonstrate with a key budget victory in the House that he can play congressional politics better than any president since Lyndon B. Johnson.

For the men closest to Reagan, the president's effective telephone lobbying and televised public appeals marked his full return to action from the March 30 assassination attempt. Yet, for all its skill and energy, Reagan's performance does not answer all the questions raised in the last two weeks.

The oldest question -- "Is Reagan up to the job?" -- had not been heard since Reagan laid it to rest in his successful campaign debate with Jimmy Carter.

Reagan's political career has followed certain patterns. One of them, a close aide pointed out last week, is that he is a performer. He triumphs in the House were quintessential examples of the contests Reagan the performer handles best, set-piece battles that he surrounds with rhetoric appealing to The American Dream.

"America was put here to expand freedom and create richer and fuller lives for its people," he told the U.S. Jaycees convention in San Antonio the day before the first House vote. "It is now in the hands of the Congress to decide which road we shall take. If we take the right road, America will once again dare to do great deeds and to reach for the impossible."

But a performer needs to be up for his performances. Reagan is better at debates, speeches and press conferences when he is doing them regularly. His skills get rusty when not used, and a senior advisor said the president had become more out of touch than even some aides realized as a result of his injury and convalescence.

Reagan reads a lot more than outsiders imagine, this aide said, but he didn't fully keep up with briefing papers and other documents during his recovery. It showed at his June 16 news conference, when he appeared unfamiliar with or unprepared for many of the foreign policy questions thrown at him.

Reagan told aides when he came off the news conference stage, "I didn't fee right. I just had a bad day."

On the morning of the news conference, Reagan walked into the Oval Office, threw down his briefing books and complained that he had been up most of the night because the White House air conditioning system provoked an allergic reaction, a senior White House official said.

Reagan's problems with the air conditioning, which also makes his voice sound hoarser and older, echo the difficulty he had with airplane air conditioning during his campaign. At one point he joked that he could campaign a lot better if they would give him a plane with an open window.

The president's men also criticize the preparation they gave him. He was given briefing books on domestic policy three days in advance, but foreign policy books only on the eve of the news conference.

The oral preparation also had its problems, an aide said. Presidential counselor Edwin Meese III, whose long, close relationship with Reagan makes him a unique briefer, was away. David Gergen, the assistant to the president for communications, who organized the briefing, "Loaded up the briefing with about 25 people so it wasn't a real briefing, but a congenial chat," he added.

If another Reagan pattern repeats, the president will get a surge of energy from his budget victory last week that will drive away the old questions of ability and age.

He is remarkably youthful 70, but at times since the bullet in his lung he has looked and sounded older. He was dragging in Iowa last year, looking old and tired. But after losing the Iowa caucuses, he won in New Hampshire and got a lift that carried him all the way to the White House.

It is not lost on the men close to Reagan, however, that the president has looked weakest on foreign policy issues. His administration continues to appear disorganized here in comparison to its performance in drafting and selling its economic program.

Reagan depends heavily for day-to-day advice on the Big Three of the White House staff, Meese, chief of staff James A. Baker III and Michael K. Deaver, but one source suggests the contrast between foreign and economic policymaking reflects the differences between Secretary of State Alexander M. Haig Jr. and Office of Management and Budget Director David A. Stockman.

Reagan sometimes feels uncomfortable with Haig because the secretary is "so bristly" and argumentative, a man close to the president said. "It would help the president on foreign policy issues if he had a smoother relationship with his secretary of state," he added, emphasizing that Reagan likes to chew over issues as he does on economics with Stockman and on every subject with the Big Three.

Stockman has put together, helped sell and helped defend a complete program to carry out the general Reagan principle of cutting federal spending. In foreign policy, Reagan has general principles (most notably his anti-Soviet stance) but there is no parallel process of making principles into working policies.

Stockman has also proved to be a team player, whereas a series of controversies involving Haig have disturbed the unified, cooperative image that Reagan seeks.

The Reagan administration set out to make its economic program its top priority and to ward off other issues that might have distracted attention. At times the administration appears to have succeeded almost too well. One top White House official conceded that Reagan has been "at no more than 70 percent" during the last few weeks despite the announcement after Memorial Day that his convalescence was finished and he was returning to full-time duty. Because he wasn't a 100 percent, this official said, he got rusty "on just about everything except the economic program."

The economic program has so dominated the first months of the administration that other issues sometimes appeared not to exist on the president's radar screen.

Meese and others dispute this. "The president has made a remarkable start," the president's counselor said. "He probably is as well or better acquainted with what's going on in the government than any other president at this time in his term."

Another White House official suggested that the president always is in good form when dealing with an issue that he can relate back to his experiences as governor of California. When an air controllers' strike was threatened, the president was very crisp and good, said this official, who watched him in meetings. "We'll put them in jail if they strike and we won't negotiate during an illegal strike," Reagan told Transportation Secretary Drew Lewis, comparing the situation to a police strike he faced when he was governor. He sent in the California Highway Patrol.

He relates his economic program to what he did in California, too, but for some issues there is no California precedent. For example, California did not have a foreign policy.

The recent polls that have shown Reagan's popularity declining have appeared to reflect a distinction between Reagan the successful performer-cheerleader and Reagan the less-successful policymaker.

Last week's Louis Harris survey found Reagan has a 60 percent favorable rating and 39 percent negative rating, but he gets much higher approval for his handling of Congress and "inspiring confidence in the White House" and lower marks for his key policy stands.

The Reagan White House system has been structured to conserve the president's time and energy. By splitting the Cabinet into smaller councils, the Reagan team has sought to make it possible for the president to participate in decision-making only when his presence is needed.

As a result, his work schedule in the White House frequently appears light. Often this month he has had only five or six meetings and his work day has ended by 2 p.m.

An exception was last Tuesday, when the president had 12 meetings scheduled.

One reason the schedule was so heavy was the last-minute addition of two or three meetings to help sell the budget program. But the main reason was that reporters for U.S. News & World Report were being allowed to follow the president, and White House officials wanted them to see a "typical day."

No one argues that Reagan must sit long hours in the Oval Office to be an effective president, and some senior White House advisers favor a "less could be more" policy of never returning to a full-time schedule.

Last week demonstrated that he has the reserves of energy if he needs them. Wednesday he flew to San Antonio, gave a speech, flew to Los Angeles and, upon learning that he had a chance to win the key procedural vote in the House, spent three hours telephoning members of Congress to win their votes.

Top aides shrug off the rough spots of the last two weeks and predict Reagan will be back in top form, buoyed by the lift he got last week.

But they also are aware that tough issues are coming up -- including the basing of the MX missiles, a manned bomber program, renewal of the Clean Air Act, immigration policy and renewal of the Voting Rights Act -- and the longer a president is in office, the more balls in the air for him to keep track of.