President Reagan's temperature returned to normal yesterday afternoon and he was said to be lively and alert as he was briefed by aides on Poland's crisis and visited by two Secret Service agents who were protecting him when he was shot.

Reagan, spending his sixth day at the George Washington University Hospital recovering from an assassination attempt last Monday, continued to "progress satisfactorily" and felt good enough to be sitting up in a chair when Secret Service agent Timothy J. McCarthy visited him at lunch, according to White House spokesmen.

Reagan rose to greet McCarthy, also recovering from a bullet wound, and told him to relay a message to his children: "You tell them this: their father put himself between me and that guy. I'm proud there are guys around to take those kinds of jobs."

Agent Jerry Parr, who pushed the president into his armored limousine at the sound of gunfire, visited Reagan earlier.

The president was described as "very alert, telling stories and laughing" during a midmorning examination by his personal physician, Dr. Daniel Ruge. His condition was said to be "good" and his temperature "only mildly elevated."

Told that the three other men wounded in Monday's assassination attempt -- McCarthy, District of Columbia police officer Thomas K. Delahanty and White House press secretary James S. Brady -- also were making progress toward recovery, Reagan said:

"That's great news, just great, especially about Jim. We'll have to get four bedpans and have a reunion."

Brady was transferred from the intensive care unit to a private room and doctors reported he was able to partially open his right eye for the first time since the shooting.

Reagan was briefed twice during the day about developments in Poland, first by White House chief of staff James A. Baker III, then later by counselor Edwin Meese III.

"The situation as we regard it bears the closest scrutiny, it bears watching," said White House deputy press secretary Larry Speaks. "It is our belief that no Soviet intervention is warranted or justifiable or imminent."

Reagan ran a temperature fluctuating from 99 to 102 degrees Friday night that doctors described as "a little bit of a setback." Doctors used a tube to remove some dormant blood particles Reagan was coughing up from his injured lung.

A White House medical bulletin said the tube was removed early yesterday and his chest X-ray showed improvement. Reagan, it said, awoke at 6:30 a.m. after a good night's sleep and had a breakfast of juice, kiwi fruit, soft boiled eggs and whole wheat toast.

The president's temperature returned to normal during the day, although he remained on antibiotics, according to a medical bulletin last night. He spent most of the day napping, visiting with his wife Nancy and her brother, Dr. Richard Davis, and taking short walks.

Reagan had a banana milkshake at 3:30 p.m., and ordered a dinner of lamb chops, yellow squash, peas, cucumber salad and banana cake.

Brady, the most seriously wounded in the shooting, "continues to make excellent progress," and his temperature fluctuations have been brought under control, the medical bulletin, said.

Brady also has begun to exhibit his well-known sense of humor. Asked by physicians yesterday what his job involved, the press secretary said, "I answer questions."

The doctor said, "Who for?"

"Anyone who asks them," Brady replied.

When the press secretary was asked why he was trying to open his eyes, which have been swollen shut by his injury, he responded, "To see who is the doctor asking all of these dumb questions."

On Friday, a doctor reported overhearing Brady complain around the sound of a ringing telephone. "Someone answer that phone, the phone's ringing," he was quoted as saying.

Yesterday's medical bulletin quoted physicians as agreeing with the thesis advanced by the FBI that the bullet that struck Brady's forehead may have exploded on impact, but it said the physicians doubted that much, if any, of the lead azide explosive contained in the bullet penetrated his skull.

In another development yesterday, the parents of John W. Hinckley Jr., accused in the shootings, said their son is "a sick boy" and asked the nation to "give him the benefit of the doubt" until the facts about his mental condition are known.

"We are joining in the prayers of millions for the president and the other victims and their families," said a statement signed by Jo Ann and Jack Hinckley of Evergreen, Colo., and released by their lawyers."We ask that you join us in prayers for our son John."

Hinckley, 25, is being held in the psychiatric unit of a federal prison at Butner, N.C., where he is undergoing up to 90 days of observation. Authorities believe Hinckley shot Reagan in a desperate attempt to win the attention of 18-year-old film star Jodie Foster.

Officials at Yale University, where Foster is a student, yesterday said federal authorities had ordered them not to discuss love letters written by Hinckley to Foster.

The actress turned the letters over to university officials last month. "University police considered them a matter of campus security and made an attempt to locate the writer of the notes in the New Haven area in order to ask him not to bother Ms. Foster any more," a Yale spokesman said.