President Reagan continued to progress toward what his doctors predicted would be "full recovery" yesterday, but physicians and aides who visited him said he was experiencing some pain and discomfort in his recuperation from his gunshot wound.

He is taking medication to relieve that pain but it is on a decreasing dosage basis, I am told," said White House chief of staff James A. Baker III.

The biggest change yesterday was improvement of the condition of White House press secretary James S. Brady, who was shot in the head in the attack that felled the president. Brady moved his left toes for the first time, counted to three and spoke simple words.

A late afternoon medical bulletin issued by Dr. Dennis O'Leary said that Brady "continues to make very satisfactory progress." Earlier, White House physician Daniel Ruge termed Brady's improvement "minimal but hopeful."

Dr. Ruge, after examining the president yesterday afternoon, issued a brief medical bulletin saying that Reagan "continues to make excellent progress toward a full recovery" and that he was experiencing normal pain for the kind of injury he had received.

Reagan was transferred from intensive care to a fourth-floor room at George Washington University Hospital. The White House took over nearly a full corridor at the hospital, converting it into a mini-office complex with space for aides, official visitors and security forces.

Meanwhile, John W. Hinckley Jr., accused of shooting the president Monday with a pistol outside the Washington Hilton Hotel, remained in confinement at the Quantico Marine Base. He is scheduled to be arraigned today on federal charges of attempting to assassinate the president and assault on a federal officer, Secret Service agent Timothy J. McCarthy.

Dr. O'Leary said that McCarthy was "doing extremely well" in his recovery. Like Reagan, he was transferred out of intensive care and into a private room at George Washington.

The condition of District of Columbia police officer Thomas K. Delahanty at the Washington Hospital Center was upgraded from fair to good. But the biggest medical news was the improvement of Brady, by far the most seriously injured of the four men wounded in the attack.

O'Leary said that Brady played catch with a small plastic ball wrapped in gauze and is responding to commands.

"There is no evidence of complications at this time," O'Leary said.

The news of Brady's improvement bolstered morale at the White House, where the press secretary is a popular figure.

"He continues to make miraculous improvement when you consider the prognosis when they brought him into the hospital," Baker said.

But while aids were happy about Brady there were signs of uneasiness for the first time at the White House since the shooting over press queries concerning the president's condition.

These concerns were sparked by at least a day's delay in a White House photograph of the president, which had been tentatively promised for yesterday. pAt the daily White House briefing, deputy press secretary Larry Speakes said the picture had been postponed for at least a day and declined to give a reason.

The reason, however, was quickly forthcoming. It was learned that Michael K. Deaver, the White House deputy chief of staff and the aide considered closest to Reagan, had determined that the president should not be photographed while he still has tubes in his arms and chest.

Baker confirmed this later in the day. Intravenous tubes that supply antibiotics were scheduled to be removed from the president's arms late last night, and a chest tube that keeps the president's left lung expanded may be removed within 24 hours.

White House sensitivity over the delay in the picture was a reminder of how traumatic the shooting was for a 70-year-old-man, despite Reagan's exceptional recovery and his hospital quips.

White House spokesman continued to assert that normal routines were being followed, with Vice President Bush picking up Reagan's meetings while reserving decisions for the president. As he did the day before, Reagan met with his top aides around his hospital bed and signed one minor measure. He also gave his approval to six administration appointments, most of them at the assistant secretary level.

Reagan Cabinet officers continued to testify before committees on Capitol Hill, trying to keep up the momentum behind the president's economic program.

Speakes said that planning continued for a scheduled Reagan trip to Mexico that would begin April 20, although the private expectations are now that the visit will have to be postponed. The White House canceled a presidential trip to Cincinnati next Wednesday, where Reagan had been scheduled to throw out the ceremonial first ball for the opening of the baseball season.

Hinckley, meanwhile, was interviewed by a court-appointed psychiatrist to see if the 25-year-old suspect is mentally competent to undergo the preliminary hearing.

The text of an unmailed letter found during a search of Hinckley's Washington hotel room was seen as evidence that the suspect had tried to kill Reagan to prove his love for a teen-age actress, Jodie Foster.

"Jodie, I would abandon this idea of getting Reagan in a second if I could only win your heart and live out the rest of my life with you whether it be in obscurity or whatever," said one passage of the letter.

Foster held a news conference in New Haven, where she attends Yale University, to acknowledge that she had received several letters from Hinckley, thrown some of them away and turned others over to her college dean who gave them to police. None of the letters mentioned the president or violence, she said.

FBI officials believe that Hinckley was obsessed with Foster and planned to kill Reagan to impress her, fashioning the assassination after a scene in "Tax Driver," in which the actress starred.

As the long legal process began, Vincent J. Fuller of the firm of Williams & Connolly was hired to defend Hinckley.

Since there were numerous eyewitnesses to the shooting, the question of Hinckley's sanity is likely to be the key issue in the case.

The Secret Service continued its own internal investigation of the shooting, trying to determine whether proper security procedures were followed Monday.

Letters of sympathy, many of them giving thanks to God that Reagan had survived the shooting, flooded the White House.

Reagan, in some discomfort, watched the Academy Awards late Tuesday night and took his first walk since Monday's surgery. He changed rooms in the morning, and walked to his new $234-a-day room aides said. Part of the cost will be borne by Reagan's own insurance from California, but the government apparently will pay the cost of staff rooms at the hospital. b

Baker said that Reagan continued to be in good spirits despite his discomfort.

"When he coughs, and they would like for him to cough, he has some pain," Baker said.

The president's wife tried to cheer him up.

Bearing jellybeans, telegrams, a bathrobe and slippers, Nancy Reagan visited her wounded husband at the hospital. Already, she is talking about his return to the White House, which could come as early as next week.

Mrs. Reagan brought a box of mints for the nurses at George Washington. She also visited Delahanty at Washington Hospital Center and told the wounded policeman, "I have a lot to thank you for."